Comma in C and C++
In C and C++, comma (, ) can be used in two contexts:
1) Comma as an operator:
The comma operator (represented by the token, ) is a binary operator that evaluates its first operand and discards the result, it then evaluates the second operand and returns this value (and type). The comma operator has the lowest precedence of any C operator, and acts as a sequence point.
2) Comma as a separator:
Comma acts as a separator when used with function calls and definitions, function like macros, variable declarations, enum declarations, and similar constructs.
The use of comma as a separator should not be confused with the use as an operator. For example, in below statement, f1() and f2() can be called in any order.
See this for C vs C++ differences of using comma operator.
You can try below programs to check your understanding of comma in C.
The following expression in the code:
a = 2, 3, 4;
is evaluated as:
(((a = 2), 3), 4);
This is because the reason that assignment operator has high precedence over the comma operator.
3) Comma operator in place of a semicolon.
We know that in C and C++, every statement is terminated with a semicolon but comma operator also used to terminate the statement after satisfying the following rules.
- The variable declaration statements must be terminated with semicolon.
- The statements after declaration statement can be terminated by comma operator.
- The last statement of the program must be terminated by semicolon.
First Line Second Line Third Line Last line
Try not to confuse between comma as a separator and comma as an operator. Sample example:
int a = 4, 3;
This will generate an error as comma in this case acts as a separator as declaration takes place. So the error less code will be as follows:
a = 4,3;
Now the value stored in a will be 3.
Also, the following is valid,
int a =(4, 3);
Again, 3 is stored in a.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.