argument, return value

//-std=c99 -Wall -Wextra -Wpedantic -Wshadow

#include <stdio.h>
#include <stdlib.h>

void f1( int *v )
{
    *v = 10;
}

void f2( int *v )
{
    f1(v);
}

int main()
{

    int val = 0;

    printf ("%d\n", val);

    f1(&val);

    printf ("%d\n\n", val);

    val = 3;

    printf ("%d\n", val);

    f2(&val);

    printf ("%d\n", val);

    return 0;
}

/*
output:

0
10

3
10

*/