Something

char *a, *b;
main()
{
a = malloc(100);
b = malloc(100);
strcpy(a, "this is a junk string");
strcpy(b, "this is a junk string");
printf("a = %p\n", a);
sprintf(a++, "%s%c", a, b[0]);
printf("a = %p\n", a);
}