To compile this source code with clang, we had to link "cs50" library like this: 
*clang hello.c -lcs50*

but we did not have to link "stdio". why? 


    /* hello.c */

    #include <stdio.h>
    #include <cs50.h>
    int main(void)
    {
        printf("state your name");
        string s = GetString();
        printf("hello, world\n");
    }