CODEWITHSUNDEEP
c
Amit Singh Tomar
Amit Singh Tomar

Reputation: 8610

Why below C code fails while compilation

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?

Upvotes: 0

Views: 140

Answers (2)

devios1
devios1

Reputation: 38025

When using variable initialization form, the comma does not act as the same operator. It is a special short-hand form for declaring multiple variables on the same line and thus requires its own syntax.

Thus in the statement int a = 1, 2, 3, the comma is actually being interpreted differently than in the statement a = 1, 2, 3.

The former is a syntax error because it doesn't meet the multiple variable declaration form. The second is valid syntax, but as others have pointed out is rather pointless because the statements 2; and 3; while syntactically correct, do nothing.

See this article on Wikipedia.

Upvotes: 0

m0skit0
m0skit0

Reputation: 25873

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().

Upvotes: 6

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