#include <stdio.h>


int main()
{
    char a[] = "Hello, world";
    extern void chop_word(char *s);

    printf("before: %s\n", a);
    chop_word(a);
    printf("after: %s\n", a);

    return 0;
}


void chop_word(char *s)
{
    for (; *s != '\0' && *s != ' '; s++)
        ;
    *s = '\0';
}