Doubt

int main(a,b,c,d,e,f,g)
{
printf("Size of a = %d\nSize of b =%d",sizeof(a),sizeof(b));
return 0;
}

The above program perfectly compiles in cygwin using gcc

and my questions are

1.How does the compiler know what are the types of variables a, b, c,
d, e, f and g?? Where is its declaration?
2.I haven't included stdio.h yet the printf compiles.The compiler
doesn't complain about the requirement of function prototype, why?
.

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