#include <stdio.h>

void changeString( char * string );

char * a;
char * b;

int main( void ) {
        /* --- */
        a = (char *)malloc( sizeof(char) * 30);
        b = (char *)malloc( sizeof(char) * 30);

        strcpy(a, "Hello, World!");
        strcpy(b, "Goodbye, Cruel World!");

        printf("%s\n", a);
        printf("%s\n", b);

        changeString(a);

        printf("%s\n", a);
        printf("%s\n", b);

        /* --- */
        return 0;
}

void changeString( char * string ) {
        /* --- */
        a=b;
        /* --- */
}