#include <stdio.h>

int xsquare ( int i )
{
    return i*i;
}

void table ( int start, int endw, int step, int (*myfunc) (int) )
{
    printf ("+-------------------+\n");
    printf ("|    x    |    y    |\n");
    printf ("+---------+---------+\n");
    
    if (step < 1)
        step=1;
    for (int i=start; i<=endw; i+=step)
    {
        printf ("| %7d | %7d |\n", i, myfunc(i));
    }
    printf ("+---------+---------+\n");
}

int main ()
{
    table ( -20, 20, 1, xsquare);
}