Why do we include stdlib.h?

Question

C function malloc() is defined under stdlib.h.

It should give an error if we don't include this file, but this code works fine with a little warning.

My question is, if malloc() works without this header file, then why do we need to include it? Please help clarify my concepts.

# include <stdio.h>

int main()  
{
    int a, b, *p;
    p = (int*)malloc(sizeof(int)*5);
    for(a=0;a<5;a++)p[a]=a*9;
    for(b=0;b<5;b++)printf("%d ",p[b]); 
}

Answer 1

In C unfortunately you don't need pre-declaration for functions. If the compiler encounters with a new function it will create an implicit declaration for it ("mmm`kay, this how it is used so I will assume that the type of the arguments are..").

Do not rely on this "feature" and in general do not write code that compiles with warnings.