Semicolon and Comma in C

Question

Why do these programs work, and why do I not get a "semicolon missing" error? With this question I want to ask about when I can skip semicolons. As far as I know semicolon is sentence terminator. Is it correct to write these type of statements where we use comma instead of semicolon? In program1 there's a negation then printing and then getchar() in one line without semicolon and using comma. Similarly in program 2, there's negation, assignment, printf and getchar() all used. How much line we can write using comma and not using semicolon?

program1:

#include <stdio.h>
int main()
{
   int i = 0xAA;
   ~i, printf("%X\n", i),getchar();
   return 0;
}

program 2:

#include <stdio.h>
int main()
{
   int i = 0xAA;
   i=~i, printf("%X\n", i),getchar();
   return 0;
}

That is the comma operator (and in the second case you get UB) — Andy Prowl, Jun 15 '13 at 19:48

score 8 · Answer 1 · answered Jun 15 '13 at 19:58

8

Why semicolon missing error is not coming in c

Because it is not missing.

answered Jun 15 '13 at 19:58

score 2 · Accepted Answer · edited May 23 '17 at 12:05

It is because the comma is an operator in C. According to the second edition of The C Programming language:

A pair of expressions separated by a comma is evaluated left to right, and the type and value of the result are the type and value of the right operand.

Be aware though, that it also says:

The commas that separate function arguments, variables in declarations etc., are not comma operators, and do not guarantee left to right evaluation.

A common example of forgetting this is explained here.

So both programs are correct (though only in the second one the inverted value of i is printed).

Semicolon and Comma in C

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