#include <stdio.h>
 
    void function1(int*); // so the compiler knows what the function looks like.
    void function2(int*);
 
    int main() {
        int varInMain = 0; // lets call it something distinct
        printf("varInMain starts with %d, it's location in memory is %p.\n",
                varInMain, &varInMain);
 
        function1(&varInMain);
 
        printf("varInMain is %d after calling function1.\n", varInMain);
 
        return 0;
    }
 
    void function1(int* func1ptr) {
        printf("function1: func1ptr points to memory location %p, which contains %d.\n",
                 func1ptr, *func1ptr);
        *func1ptr = 1010;
        function2(func1ptr);
    }
 
    void function2(int* func2ptr) {
        printf("function2: func2ptr points to memory location %p, which contains %d.\n",
                 func2ptr, *func2ptr);
        *func2ptr = 123;
    }
 

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