Question

I have a C code ,which uses simple comma operators

main()
{
int a= 1,2,3;
printf("%d",a);
}

Now when i compile got an error while same program with little modification runs fine

main()
{
int a;
    a= 1,2,3;
    printf("%d",a);
}

Why is it so?

Answer 1

In the first case, the error is raised because the compiler is not able to differentiate if you pretend to declare several variables or assign several values.

int a= 1,2,3; 

Did you mean int a; a = 1, 2, 3, or int a = 1, int 2, int 3? Compiler cannot tell from context (even if 2 or 3 are not legal variable names).

This ambiguity does not exist in the second case, hence no error (but warnings issued anyway).

PS: it’s int main() not void main().