Question

I don’t get this part. How can I do it if I’m not allowed to use global variables? Example:

main()
{ int z;
  function1(&z);
}

function1(int *x)
{
  function2(&x);
}

function2(int *number)
{
   ++(*number);
}

Answer 1

When function1 calls function2, just pass in x, not &x.

function1(int *x)
{
  function2(x); /* not &x */
}

&x will pass function2 a pointer to a pointer to an int, but it is declared to only take a pointer to an int.

Other issues: z should be initialized, and the functions should either have forward declarations, are declared above main. main should be declared to return an int, and return 0 on success. And as noted in the other answer, your other functions also need return types.

void function2(int *number)
{
   ++(*number);
}

void function1(int *x)
{
  function2(x);
}

int main()
{
  int z = 0;
  function1(&z);
  return 0;
}