multiple assignments c

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C structures, c reference, c declare multiple variables, declare multiple variables.

To declare more than one variable of the same type, use a comma-separated list:

You can also assign the same value to multiple variables of the same type:

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Fill in the missing parts to create three variables of the same type, using a comma-separated list :

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Assignment Operators in C

Assignment operators are used for assigning value to a variable. The left side operand of the assignment operator is a variable and right side operand of the assignment operator is a value. The value on the right side must be of the same data-type of the variable on the left side otherwise the compiler will raise an error.

Different types of assignment operators are shown below:

1. “=”: This is the simplest assignment operator. This operator is used to assign the value on the right to the variable on the left. Example:

2. “+=” : This operator is combination of ‘+’ and ‘=’ operators. This operator first adds the current value of the variable on left to the value on the right and then assigns the result to the variable on the left. Example:

If initially value stored in a is 5. Then (a += 6) = 11.

3. “-=” This operator is combination of ‘-‘ and ‘=’ operators. This operator first subtracts the value on the right from the current value of the variable on left and then assigns the result to the variable on the left. Example:

If initially value stored in a is 8. Then (a -= 6) = 2.

4. “*=” This operator is combination of ‘*’ and ‘=’ operators. This operator first multiplies the current value of the variable on left to the value on the right and then assigns the result to the variable on the left. Example:

If initially value stored in a is 5. Then (a *= 6) = 30.

5. “/=” This operator is combination of ‘/’ and ‘=’ operators. This operator first divides the current value of the variable on left by the value on the right and then assigns the result to the variable on the left. Example:

If initially value stored in a is 6. Then (a /= 2) = 3.

Below example illustrates the various Assignment Operators:

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Assignment Operators in C

In C language, the assignment operator stores a certain value in an already declared variable. A variable in C can be assigned the value in the form of a literal, another variable, or an expression.

The value to be assigned forms the right-hand operand, whereas the variable to be assigned should be the operand to the left of the " = " symbol, which is defined as a simple assignment operator in C.

In addition, C has several augmented assignment operators.

The following table lists the assignment operators supported by the C language −

Operator	Description	Example
=	Simple assignment operator. Assigns values from right side operands to left side operand	C = A + B will assign the value of A + B to C
+=	Add AND assignment operator. It adds the right operand to the left operand and assign the result to the left operand.	C += A is equivalent to C = C + A
-=	Subtract AND assignment operator. It subtracts the right operand from the left operand and assigns the result to the left operand.	C -= A is equivalent to C = C - A
*=	Multiply AND assignment operator. It multiplies the right operand with the left operand and assigns the result to the left operand.	C = A is equivalent to C = C A
/=	Divide AND assignment operator. It divides the left operand with the right operand and assigns the result to the left operand.	C /= A is equivalent to C = C / A
%=	Modulus AND assignment operator. It takes modulus using two operands and assigns the result to the left operand.	C %= A is equivalent to C = C % A
<<=	Left shift AND assignment operator.	C <<= 2 is same as C = C << 2
>>=	Right shift AND assignment operator.	C >>= 2 is same as C = C >> 2
&=	Bitwise AND assignment operator.	C &= 2 is same as C = C & 2
^=	Bitwise exclusive OR and assignment operator.	C ^= 2 is same as C = C ^ 2
\|=	Bitwise inclusive OR and assignment operator.	C \|= 2 is same as C = C \| 2

Simple Assignment Operator (=)

The = operator is one of the most frequently used operators in C. As per the ANSI C standard, all the variables must be declared in the beginning. Variable declaration after the first processing statement is not allowed.

You can declare a variable to be assigned a value later in the code, or you can initialize it at the time of declaration.

You can use a literal, another variable, or an expression in the assignment statement.

Once a variable of a certain type is declared, it cannot be assigned a value of any other type. In such a case the C compiler reports a type mismatch error.

In C, the expressions that refer to a memory location are called "lvalue" expressions. A lvalue may appear as either the left-hand or right-hand side of an assignment.

On the other hand, the term rvalue refers to a data value that is stored at some address in memory. A rvalue is an expression that cannot have a value assigned to it which means an rvalue may appear on the right-hand side but not on the left-hand side of an assignment.

Variables are lvalues and so they may appear on the left-hand side of an assignment. Numeric literals are rvalues and so they may not be assigned and cannot appear on the left-hand side. Take a look at the following valid and invalid statements −

Augmented Assignment Operators

In addition to the = operator, C allows you to combine arithmetic and bitwise operators with the = symbol to form augmented or compound assignment operator. The augmented operators offer a convenient shortcut for combining arithmetic or bitwise operation with assignment.

For example, the expression "a += b" has the same effect of performing "a + b" first and then assigning the result back to the variable "a".

Run the code and check its output −

Similarly, the expression "a <<= b" has the same effect of performing "a << b" first and then assigning the result back to the variable "a".

Here is a C program that demonstrates the use of assignment operators in C −

When you compile and execute the above program, it will produce the following result −

Next: Conditional Expression , Previous: Logicals and Comparison , Up: Execution Control Expressions [ Contents ][ Index ]

8.3 Logical Operators and Assignments

There are cases where assignments nested inside the condition can actually make a program easier to read. Here is an example using a hypothetical type list which represents a list; it tests whether the list has at least two links, using hypothetical functions, nonempty which is true if the argument is a nonempty list, and list_next which advances from one list link to the next. We assume that a list is never a null pointer, so that the assignment expressions are always “true.”

Here we take advantage of the ‘ && ’ operator to avoid executing the rest of the code if a call to nonempty returns “false.” The only natural place to put the assignments is among those calls.

It would be possible to rewrite this as several statements, but that could make it much more cumbersome. On the other hand, when the test is even more complex than this one, splitting it into multiple statements might be necessary for clarity.

If an empty list is a null pointer, we can dispense with calling nonempty :

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6.1. Multiple assignment ¶

I haven’t said much about it, but it is legal in C++ to make more than one assignment to the same variable. The effect of the second assignment is to replace the old value of the variable with a new value.

The active code below reassigns fred from 5 to 7 and prints both values out.

The output of this program is 57 , because the first time we print fred his value is 5, and the second time his value is 7.

The active code below reassigns fred from 5 to 7 without printing out the initial value.

However, if we do not print fred the first time, the output is only 7 because the value of fred is just 7 when it is printed.

This kind of multiple assignment is the reason I described variables as a container for values. When you assign a value to a variable, you change the contents of the container, as shown in the figure:

When there are multiple assignments to a variable, it is especially important to distinguish between an assignment statement and a statement of equality. Because C++ uses the = symbol for assignment, it is tempting to interpret a statement like a = b as a statement of equality. It is not!

An assignment statement uses a single = symbol. For example, x = 3 assigns the value of 3 to the variable x . On the other hand, an equality statement uses two = symbols. For example, x == 3 is a boolean that evaluates to true if x is equal to 3 and evaluates to false otherwise.

First of all, equality is commutative, and assignment is not. For example, in mathematics if $a = 7$ then $7 = a$ . But in C++ the statement a = 7; is legal, and 7 = a; is not.

Furthermore, in mathematics, a statement of equality is true for all time. If $a = b$ now, then $a$ will always equal $b$ . In C++, an assignment statement can make two variables equal, but they don’t have to stay that way!

The third line changes the value of a but it does not change the value of b , and so they are no longer equal. In many programming languages an alternate symbol is used for assignment, such as <- or := , in order to avoid confusion.

Although multiple assignment is frequently useful, you should use it with caution. If the values of variables are changing constantly in different parts of the program, it can make the code difficult to read and debug.

Checking if a is equal to b
Assigning a to the value of b
Setting the value of a to 4

Q-4: What will print?

There are no spaces between the numbers.
Remember, in C++ spaces must be printed.
Carefully look at the values being assigned.

Q-5: What is the correct output?

Remember that printing a boolean results in either 0 or 1.
Is x equal to y?
x is equal to y, so the output is 1.

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How expression a=b=c (Multiple Assignment) evaluates in C programming?

Since C language does not support chaining assignment like a=b=c ; each assignment operator ( = ) operates on two operands only. Then how expression a=b=c evaluates?

According to operators associativity assignment operator ( = ) operates from right to left, that means associativity of assignment operator ( = ) is right to left.

Expression a=b=c is actually a=(b=c) , see how expression a=(b=c) evaluates?

Value of variable c will be assigned into variable b first.
Then value of variable b will be assigned into variable a .

Finally value of variables a and b will be same as the value of variable c .

Consider the following program

Assigning a value to multiple variables of same type

By using such kind of expression we can easily assign a value to multiple variables of same data type, for example - if we want to assign 0 to integer variables a , b , c and d ; we can do it by following expression:

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Assignment operators.















(C11)









Miscellaneous

General




(C11)







(C99)

Assignment and compound assignment operators are binary operators that modify the variable to their left using the value to their right.

Operator	Operator name	Example	Description	Equivalent of
=	basic assignment	a = b	becomes equal to
+=	addition assignment	a += b	becomes equal to the addition of and	a = a + b
-=	subtraction assignment	a -= b	becomes equal to the subtraction of from	a = a - b
*=	multiplication assignment	a *= b	becomes equal to the product of and	a = a * b
/=	division assignment	a /= b	becomes equal to the division of by	a = a / b
%=	modulo assignment	a %= b	becomes equal to the remainder of divided by	a = a % b
&=	bitwise AND assignment	a &= b	becomes equal to the bitwise AND of and	a = a & b
\|=	bitwise OR assignment	a \|= b	becomes equal to the bitwise OR of and	a = a \| b
^=	bitwise XOR assignment	a ^= b	becomes equal to the bitwise XOR of and	a = a ^ b
<<=	bitwise left shift assignment	a <<= b	becomes equal to left shifted by	a = a << b
>>=	bitwise right shift assignment	a >>= b	becomes equal to right shifted by	a = a >> b

Simple assignment Notes Compound assignment References See Also See also

[ edit ] Simple assignment

The simple assignment operator expressions have the form


lhs rhs

lhs	-	expression of any complete object type
rhs	-	expression of any type to lhs or with lhs

Assignment performs implicit conversion from the value of rhs to the type of lhs and then replaces the value in the object designated by lhs with the converted value of rhs .

Assignment also returns the same value as what was stored in lhs (so that expressions such as a = b = c are possible). The value category of the assignment operator is non-lvalue (so that expressions such as ( a = b ) = c are invalid).

rhs and lhs must satisfy one of the following:

both lhs and rhs have compatible struct or union type, or..
rhs must be implicitly convertible to lhs , which implies
both lhs and rhs have arithmetic types , in which case lhs may be volatile -qualified or atomic (since C11)
both lhs and rhs have pointer to compatible (ignoring qualifiers) types, or one of the pointers is a pointer to void, and the conversion would not add qualifiers to the pointed-to type. lhs may be volatile or restrict (since C99) -qualified or atomic (since C11) .
lhs is a (possibly qualified or atomic (since C11) ) pointer and rhs is a null pointer constant such as NULL or a nullptr_t value (since C23)

has type (possibly qualified or atomic(since C11)) _Bool and rhs is a pointer or a value(since C23)

(since C99)

has type (possibly qualified or atomic) and rhs has type

(since C23)

[ edit ] Notes

If rhs and lhs overlap in memory (e.g. they are members of the same union), the behavior is undefined unless the overlap is exact and the types are compatible .

Although arrays are not assignable, an array wrapped in a struct is assignable to another object of the same (or compatible) struct type.

The side effect of updating lhs is sequenced after the value computations, but not the side effects of lhs and rhs themselves and the evaluations of the operands are, as usual, unsequenced relative to each other (so the expressions such as i = ++ i ; are undefined)

Assignment strips extra range and precision from floating-point expressions (see FLT_EVAL_METHOD ).

In C++, assignment operators are lvalue expressions, not so in C.

[ edit ] Compound assignment

The compound assignment operator expressions have the form


lhs op rhs

op	-	one of *=, /= %=, += -=, <<=, >>=, &=, ^=, \|=
lhs, rhs	-	expressions with (where lhs may be qualified or atomic), except when op is += or -=, which also accept pointer types with the same restrictions as + and -

The expression lhs @= rhs is exactly the same as lhs = lhs @ ( rhs ) , except that lhs is evaluated only once.

If lhs has type, the operation behaves as a single atomic read-modify-write operation with memory order .

For integer atomic types, the compound assignment @= is equivalent to:

addr = &lhs; T2 val = rhs; T1 old = *addr; T1 new; do { new = old @ val } while (! (addr, &old, new);

(since C11)

[ edit ] References

C17 standard (ISO/IEC 9899:2018):
6.5.16 Assignment operators (p: 72-73)
C11 standard (ISO/IEC 9899:2011):
6.5.16 Assignment operators (p: 101-104)
C99 standard (ISO/IEC 9899:1999):
6.5.16 Assignment operators (p: 91-93)
C89/C90 standard (ISO/IEC 9899:1990):
3.3.16 Assignment operators

[ edit ] See Also

Operator precedence

Common operators

a = b a += b a -= b a *= b a /= b a %= b a &= b a \|= b a ^= b a <<= b a >>= b	++a --a a++ a--	+a -a a + b a - b a * b a / b a % b ~a a & b a \| b a ^ b a << b a >> b	!a a && b a \|\| b	a == b a != b a < b a > b a <= b a >= b	a[b] *a &a a->b a.b	a(...) a, b (type) a a ? b : c sizeof _Alignof (since C11)

[ edit ] See also

for Assignment operators

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5.1. Multiple assignment ¶

I haven’t said much about it, but it is legal in C++ to assign to the same variable more than once. The effect of the second assignment is to replace the old value of the variable with a new value.

The code below reassigns fred from 5 to 7 and prints both values out.

The output of this program is 57 , because the first time we print fred his value is 5, and the second time his value is 7.

The active code below reassigns fred from 5 to 7 without printing out the initial value.

However, if we do not print fred the first time, the output is only 7 because the value of fred is just 7 when it is printed.

This kind of multiple assignment is the reason I described variables as a container for values. When you assign a value to a variable, you change the contents of the existing storage location, as shown in the codelens below. Step through the code one line at a time and notice how the value assigned to fred changes even when no output is created.

Activity: CodeLens Reassigning values to fred (multiple_assignment_CL)

This is a common source of error.

First of all, equality is commutative, and assignment is not. For example, in mathematics if $a = 7$ then $7 = a$ . But in C++ the statement a = 7; is legal, and 7 = a; is not.

Checking if a is equal to b
Assigning a to the value of b
Setting the value of a to 4

Q-5: What will print?

There are no spaces between the numbers.
Remember, in C++ spaces must be printed.
Carefully look at the values being assigned.

Q-6: What is the correct output?

Remember that printing a boolean results in either 0 or 1.
Is x equal to y?
x is equal to y, so the output is 1.

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Why declare a variable in one line, and assign to it in the next?

I often see in C and C++ code the following convention:

I initially assumed that this was a habit left over from the days when you had to declare all local variables at the top of the scope. But I've learned not to dismiss so quickly the habits of veteran developers. So, is there a good reason for declaring in one line, and assigning afterwards?

15 +1 for "I've learned not to dismiss so quickly the habits of veteran developers." That's a wise lesson to learn. – Wildcard Commented Nov 30, 2015 at 15:56

7 Answers 7

In C89 all declarations had to be be at the beginning of a scope ( { ... } ), but this requirement was dropped quickly (first with compiler extensions and later with the standard).

These examples are not the same. some_type val = something; calls the copy constructor while val = something; calls the default constructor and then the operator= function. This difference is often critical.

Some people prefer to first declare variables and later define them, in the case they are reformatting their code later with the declarations in one spot and the definition in an other.

About the pointers, some people just have the habit to initialize every pointer to NULL or nullptr , no matter what they do with that pointer.

1 Great distinction for C++, thanks. What about in plain C? – Jonathan Sterling Commented May 7, 2011 at 20:35
14 The fact that MSVC still doesn't support declarations except at the beginning of a block when it's compiling in C mode is the source of endless irritation for me. – Michael Burr Commented May 7, 2011 at 22:03
5 @Michael Burr: This is because MSVC doesn't support C99 at all. – orlp Commented May 7, 2011 at 22:05
4 "some_type val = something; calls the copy constructor": it may call the copy constructor, but the Standard allows the compiler to elide the default-construction of a tempory, copy construction of val and destruction of the temporary and directly construct val using a some_type constructor taking something as sole argument. This is a very interesting and unusual edge case in C++... it means there's a presumption about the semantic meaning of these operations. – Tony Commented May 9, 2011 at 9:15
2 @Aerovistae: for built-in types they are the same, but the same can not always be said for user-defined types. – orlp Commented Oct 11, 2012 at 18:48

You have tagged your question C and C++ at the same time, while the answer is significantly different in these languages.

Firstly, the wording of the title of your question is incorrect (or, more precisely, irrelevant to the question itself). In both of your examples the variable is declared and defined simultaneously, in one line. The difference between your examples is that in the first one the variables are either left uninitialized or initialized with a dummy value and then it is assigned a meaningful value later. In the second example the variables are initialized right away.

Secondly, in C++ language, as @nightcracker noted in his answer these two constructs are semantically different. The first one relies on initialization while the second one - on assignment. In C++ these operations are overloadable and therefore can potentially lead to different results (although one can note that producing non-equivalent overloads of initialization and assignment is not a good idea).

In the original standard C language (C89/90) it is illegal to declare variables in the middle of the block, which is why you might see variables declared uninitialized (or initialized with dummy values) at the beginning of the block and then assigned meaningful values later, when those meaningful values become available.

In C99 language it is OK to declare variables in the middle of the block (just like in C++), which means that the first approach is only needed in some specific situations when the initializer is not known at the point of declaration. (This applies to C++ as well).

2 @Jonathan Sterling: I read your examples. You probably need to brush up on the standard terminology of C and C++ languages. Specifically, on the terms declaration and definition , which have specific meanings in these languages. I'll repeat it again: in both of your examples the variables are declared and defined in one line. In C/C++ the line some_type val; immediately declares and defines the variable val . This is what I meant in my answer. – AndreyT Commented May 7, 2011 at 20:53
1 I see what you mean there. You're definitely right about declare and define being rather meaningless the way I used them. I hope you accept my apologies for the poor wording, and poorly-thought-out comment. – Jonathan Sterling Commented May 7, 2011 at 20:55
1 So, if the consensus is that “declare” is the wrong word, I'd suggest that someone with a better knowledge of the standard than me edit the Wikibooks page. – Jonathan Sterling Commented May 7, 2011 at 21:11
2 In any other context declare would be the right word, but since declare is a well-defined concept , with consequences, in C and C++ you can not use it as loosely as you could in other contexts. – orlp Commented May 7, 2011 at 21:15
2 @ybungalobill: You are wrong. Declaration and definition in C/C++ is not mutually exclusive concepts. Actually, definition is just a specific form of declaration . Every definition is a declaration at the same time (with few exceptions). There are defining declarations (i.e. definitions) and non-defining declarations. Moreover, normally the therm declaration is used all the time (even if it is a definition), except for the contexts when the distinction between the two is critical. – AndreyT Commented May 7, 2011 at 21:52

I think it's an old habit, leftover from "local declaration" times. And therefore as answer to your question: No I don't think there's a good reason. I never do it myself.

I said something about that in my answer to a question by Helium3 .

Basically, I say it's a visual aid to easily see what is changed.

The other answers are pretty good. There's some history around this in C. In C++ there's the difference between a constructor and an assignment operator.

I'm surprised no one mentions the additional point: keeping declarations separate from use of a variable can sometimes be a lot more readable.

Visually speaking, when reading code, the more mundane artifacts, such as the types and names of variables, are not what jump out at you. It's the statements that you're usually most interested in, spend most time staring at, and so there's a tendency to glance over the rest.

If I have some types, names, and assignment all going on in the same tight space, it's a bit of information overload. Further, it means that something important is going on in the space that I usually glance over.

It may seem a bit counter-intuitive to say, but this is one instance where making your source take up more vertical space can make it better. I see this as akin to why you shouldn't write jam-packed lines which do crazy amounts of pointer arithmetic and assignment in a tight vertical space -- just because the language lets you get away with such things doesn't mean you should do it all the time. :-)

In C, this was the standard practice because variables had to be declared at the start of the function, unlike in C++, where it could be declared anywhere in the function body to be used thereafter. Pointers were set to 0 or NULL, because it just made sure that the pointer pointed to no garbage. Otherwise, there's no significant advantage that I can think of, which compels anyone to do like that.

Pros for localising variable definitions and their meaningful initialisation:

if variables are habitually assigned a meaningful value when they first appear in the code (another perspective on the same thing: you delay their appearance until a meaningful value is avaialable) then there's no chance of them accidentally being used with a meaningless or uninitialised value (which can easily happen is some initialisation is accidentally bypassed due to conditional statements, short-circuit evaluation, exceptions etc.)

can be more efficient

avoids overheads of setting initial value (default construction or initialisation to some sentinel value like NULL)
operator= can sometimes be less efficient and require a temporary object
sometimes (esp. for inline functions) the optimiser can remove some/all inefficiencies

minimising the scope of variables in turn minimises average number of variables concurrently in scope : this

makes it easier to mentally track the variables in scope, the execution flows and statements that might affect those variables, and the import of their value
at least for some complex and opaque objects, this reduces resource usage (heap, threads, shared memory, descriptors) of the program

sometimes more concise as you're not repeating the variable name in a definition then in an initial meaningful assignment

necessary for certain types such as references and when you want the object to be const

Arguments for grouping variable definitions:

sometimes it's convenient and/or concise to factor out the type of a number of variables:

the_same_type v1, v2, v3;

(if the reason is just that the type name is overly long or complex, a typedef can sometimes be better)

sometimes it's desirable to group variables independently of their usage to emphasise the set of variables (and types) involved in some operation:

type v1; type v2; type v3;

This emphasises the commonality of type and makes it a little easier to change them, while still sticking to a variable per line which facilitates copy-paste, // commenting etc..

As is often the case in programming, while there can be a clear empirical benefit to one practice in most situations, the other practice really can be overwhelmingly better in a few cases.

I wish more languages would distinguish the case where code declares and sets the value of a variable which would never be written elsewhere, though new variables could use the same name [i.e. where behavior would be the same whether the later statements used the same variable or a different one], from those where code creates a variable that must be writable in multiple places. While both use cases will execute the same way, knowing when variables may change is very helpful when trying to track down bugs. – supercat Commented Apr 28, 2014 at 22:50

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Multiple Assignment

Multiple Assignment

No, that assigns a, b, and c to c+5.

Xerzi's way is better. Mines is a sloppy version to do that. Pretty sure it doesn't get easier than that but if anyone finds a better solution i'll be curious to see it.

elipses( count, ...) { (count<=0) { 0; } va_list arg_ptr; va_start(arg_ptr, count); sum=0; ( i=0; i<count; i++) sum += va_arg(arg_ptr, ); va_end(arg_ptr); sum; }

C++ Operators Introduction

C++ multiple assignments, c++ arithmetic operators, c++ relational operators, c++ logical operators, c++ relational logical precedence, c++ increment and decrement, c++ assignment operator, c++ compound assignment, c++ conditional operator, c++ logical operators in if, c++ bitwise operators introduction, c++ bitwise shift operators, c++ bitwise operators usage, c++ comma operator, c++ operator precedence, c++ sizeof operator, c++ operators new and delete, c++ allocating arrays, c++ memory initializing, c++ malloc() and free(), c++ operator exercise 1.

C++ allows a very convenient method of assigning many variables the same value: using multiple assignments in a single statement.

For example, this fragment assigns count, incr, and index the value 10:

In professionally written programs, you will often see variables assigned a common value using this format.

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c# multi assignment

This sort of thing would be really helpfull in C#. In this example 'a' and 'b' arn't encapsulated together such as the X and Y of a position might be. Does this exist in some form?

Below is a less trivial example.

Adam Maras shows in the comments that:

Sort of works for the example above however as he then points out it creates a new truple instead of changing the specified values.

Eric Lippert asks for use cases, therefore perhaps:

notallama also has use cases, they are in his answer below.

variable-assignment

11 The last statement looks really unreadable to me. – BoltClock Commented Nov 28, 2011 at 17:40
1 I think this is more readable int a = 2; int b = 3; – JonH Commented Nov 28, 2011 at 17:42
1 @JonH: int a = 2, b = 3; optionally replacing the space after the comma with a line break. – BoltClock Commented Nov 28, 2011 at 17:42
4 Use F#, it's more suited for this kind of things – Nasreddine Commented Nov 28, 2011 at 17:47
1 Hey, I like this idea! Especially for out vars! – Arlen Beiler Commented May 9, 2013 at 19:40

7 Answers 7

We have considered supporting a syntactic sugar for tuples but it did not make the bar for C# 4.0. It is unlikely to make the bar for C# 5.0; the C# 5.0 team is pretty busy with getting async/await working right. We will consider it for hypothetical future versions of the language.

If you have a really solid usage case that is compelling, that would help us prioritize the feature.

6 Most methods that use 'out' parameters would be more readable and concise if they were re-written using multiple assignment. The compiler warning "The out parameter 'x' must be assigned to before control leaves the current method" indicates how error-prone out vars can be—if you instead had to specify all the return vars in the return statement that would be a nice, self-reinforcing way for programmers to know they're doing the right thing. – user87453 Commented Mar 26, 2012 at 0:12
2 IMHO, after playing with Scala a bit and having read about how other languages deal with this, I now find the C# approach on tuples really cheap and ugly. I'm really looking forward to see this feature fully implemented in the language or at least some syntactic sugar added. As it stands now it feels like a half baked feature to me. – Trap Commented Oct 15, 2012 at 11:42
2 Those of us whose programming is more mathematical in nature very much appreciate multiple assignment / tuple support in the language. I recently made extensive use of F# because of this, using only C# in places where I had to interact with COM code, because F# let us more or less transliterate the formalisms from our paper straight into code. I would love to have these features in C#, as would my collaborators who are less comfortable in functional languages than I am. – Dan Barowy Commented Jul 19, 2013 at 21:11
2 @DanBarowy: Indeed, F# is often praised for exactly this property; C# by contrast has much more "ceremony" around it. I am no longer in a position to strongly influence the feature set for hypothetical future versions, but I do know that Anders and Mads and the other designers are aware that this is a pain point. – Eric Lippert Commented Jul 19, 2013 at 22:39
1 "it did not make the bar for C# 4.0". "pretty busy with getting async/await working right". double baffle. – nicolas Commented Oct 16, 2013 at 14:30

it'd be really nice for working with IObservables, since those have only one type parameter. you basically want to subscribe with arbitrary delegates, but you're forced to use Action, so that means if you want multiple parameters, you have to either use tuples, or create custom classes for packing and unpacking parameters.

example from a game:

which i think is cleaner.

also, presumably IAsyncResult will have similar issues when you want to pass several values. sometimes it's cumbersome to create classes just to shuffle a bit of data around, but using tuples as they are now reduces code clarity. if they're used in the same function, anonymous types fit the bill nicely, but they don't work if you need to pass data between functions.

also, it'd be nice if the sugar worked for generic parameters, too. so:

would desugar to

The behavior that you're looking for can be found in languages that have support or syntactic sugar for tuples . C# is not among these langauges; while you can use the Tuple<...> classes to achieve similar behavior, it will come out very verbose (not clean like you're looking for.)

1 var tuple = Tuple.Create(2, 3); It's not too terrible. – Dismissile Commented Nov 28, 2011 at 17:51
1 No, but it's not as fluent as (for example) a lot of functional languages make working with tuples. – Adam Maras Commented Nov 28, 2011 at 17:54
Can you rewrite the 2nd example using tuple and var? – alan2here Commented Nov 28, 2011 at 17:58
2 var result = n == 4 ? Tuple.Create(2, 3) : Tuple.Create(3, n % 2 == 0 ? 1 : 2); (off the top of my head, might not be quite right) – Adam Maras Commented Nov 28, 2011 at 18:06
1 Mind you, that's not congruent to your sample, as you're creating a new tuple instead of considering a and b as parts of an implicit tuple. You'd then have to assign the result of each part of the tuple to a and b afterwards, or just reference the tuple instead. – Adam Maras Commented Nov 28, 2011 at 18:08

Deconstruction was introduced in C# 7.0: https://blogs.msdn.microsoft.com/dotnet/2016/08/24/whats-new-in-csharp-7-0/#user-content-deconstruction

The closest structure I can think of is the Tuple class in version 4.0 of the framework.

As others already wrote, C# 4 Tuples are a nice addition, but nothing really compelling to use as long as there aren't any unpacking mechanisms. What I really demand of any type I use is clarity of what it describes, on both sides of the function protocol (e.g. caller, calle sides)... like

This is obvious and clear at both caller and callee side. However this

Doesn't leave the slightest clue about what that solution actually is (ok, the string and the method name make it pretty obvious) at the call site. Item1 and Item2 are of the same type, which renders tooltips useless. The only way to know for certain is to "reverse engineer" your way back through SolvePQ .

Obivously, this is far fetched and everyone doing serious numerical stuff should have a Complex type (like that in the BCL). But everytime you get split results and you want give those results distinct names for the sake of readability , you need tuple unpacking. The rewritten last two lines would be:

This leaves no room for confusion, except for getting used to the syntax.

Creating a set of Unpack<T1, T2>(this Tuple<T1, T2>, out T1, out T2) methods would be a more idiomatic c# way of doing this.

Your example would then become

which is no more complex than your proposal, and a lot clearer.

2 First, with that technique you can't use var to infer the type of a and b, and secondly it's a whole lot more verbose than just (a, b) = (2, 3) . Not saying your proposal is bad, just that it's not as good as what a full language integration of tuples could be. – Suzanne Soy Commented Jun 30, 2014 at 14:56
Languages with integral support for tuples are really nice to work with, but I don't believe that c# should be such a language. In my opinion, the added verbosity is desirable, because any programmer with even a basic understanding of c# syntax (or rusty, inattentive, etc) instantly and intuitively knows what that line means. – Ivy Gorven Commented Jul 13, 2014 at 10:12

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In C++ assignment evaluates to an lvalue, which requires "chained" assignments to be sequenced.) There's no way to say whether it is a good or bad programming practice without seeing more context. In cases when the two variables are tightly related (like x and y coordinate of a point), setting them to some common value using "chained ...
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1. "=": This is the simplest assignment operator. This operator is used to assign the value on the right to the variable on the left. Example: a = 10; b = 20; ch = 'y'; 2. "+=": This operator is combination of '+' and '=' operators. This operator first adds the current value of the variable on left to the value on the right and ...
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6.1. Multiple assignment
6.1. Multiple assignment ¶. I haven't said much about it, but it is legal in C++ to make more than one assignment to the same variable. The effect of the second assignment is to replace the old value of the variable with a new value. The active code below reassigns fred from 5 to 7 and prints both values out. Save & Run.
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Assignment performs implicit conversion from the value of rhs to the type of lhs and then replaces the value in the object designated by lhs with the converted value of rhs. Assignment also returns the same value as what was stored in lhs (so that expressions such as a = b = c are possible). The value category of the assignment operator is non ...
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C. In C89 all declarations had to be be at the beginning of a scope ({ ... }), but this requirement was dropped quickly (first with compiler extensions and later with the standard).. C++. These examples are not the same. some_type val = something; calls the copy constructor while val = something; calls the default constructor and then the operator= function.
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No, that assigns a, b, and c to c+5. try parenthesizing the "c+=5". No, that assigns a, b, and c to c+5. I did it that way because you were adding the same values to them (5) and they all started with the same values (10) That is starting to look more like a recursive operation than variable assignment.
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The proper way doing this is just. std::swap(a, b); Boost includes a tuple class with which you can do. tie(a, b) = make_tuple(b, a); It internally creates a tuple of references to a and b, and then assigned to them a tuple of b and a. answered Nov 8, 2008 at 20:27. Johannes Schaub - litb. 505k 131 913 1.2k.
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a, b = 0, 1. while a < 10: print(a) a, b = b, a+b. With the multiple assignment, set initial values as a=0, b=1. In the while loop, both elements are assigned new values (hence called 'multiple' assignment). View it as (a,b) = (b,a+b). So a = b, b = a+b at each iteration of the loop. This continues while a<10.
.net
Those of us whose programming is more mathematical in nature very much appreciate multiple assignment / tuple support in the language. I recently made extensive use of F# because of this, using only C# in places where I had to interact with COM code, because F# let us more or less transliterate the formalisms from our paper straight into code.

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Assignment Operators in C

Simple Assignment Operator (=)

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8.3 Logical Operators and Assignments

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6.1. Multiple assignment ¶

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How expression a=b=c (Multiple Assignment) evaluates in C programming?

Assigning a value to multiple variables of same type

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