Changing address contained by pointer using function

Question

If I\'ve declared a pointer p as int *p; in main module, I can change the address contained by p by assigning p=&a; w

Answer 1

For a primitive data type such as an int, the double pointers are not necessary. You can write directly into the address where the int is stored, treating its address as a pointer in the function being called. This is unlike a char array ("string") where the size of what is pointed to is variable and you must therefore use another level of indirection when changing it from within a called function. Try this:

void foo(int *oldVal)
{
    int newVal = 99;    // or whatever you want
    *oldVal = newVal;
}

int main(int argc, char *argv[])
{
    int someVal = 0;
    foo(&someVal);      // we send its address to foo()

    printf("someVal is now %d.\n", someVal);

    return EXIT_SUCCESS;
}