Using a look-up table (demo)

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
// Function prototypes
int main();
int multi(int, int);
// Array used as a look-up table:
int multiply[12][12]=
{
     1,   2,   3,   4,   5,   6,   7,   8,   9,  10,  11,  12,
     2,   4,   6,   8,  10,  12,  14,  16,  18,  20,  22,  24,
     3,   6,   9,  12,  15,  18,  21,  24,  27,  30,  33,  36,
     4,   8,  12,  16,  20,  24,  28,  32,  36,  40,  44,  48,
     5,  10,  15,  20,  25,  30,  35,  40,  45,  50,  55,  60,
     6,  12,  18,  24,  30,  36,  42,  48,  54,  60,  66,  72,
     7,  14,  21,  28,  35,  42,  49,  56,  63,  70,  77,  84,
     8,  16,  24,  32,  40,  48,  56,  64,  72,  80,  88,  96,
     9,  18,  27,  36,  45,  54,  63,  72,  81,  90,  99, 108,
    10,  20,  30,  40,  50,  60,  70,  80,  90, 100, 110, 120,
    11,  22,  33,  44,  55,  66,  77,  88,  99, 110, 121, 132,
    12,  24,  36,  48,  60,  72,  84,  96, 108, 120, 132, 144
};
// Global variables:
int i=0;
int c=0;
int main()
{
    system("cls");
    // printf("Using an array as a look-up table:\n");
    for(i=0; i<13; i=i+1)
    {
        for(c=0; c<13; c=c+1)
        {
            printf("%d x %d = %d\n",i,c,multi(i,c));
        }
    }
    return 0;
}
int multi(int x, int y)
{
    // Checks for multiplication by zero...
    if(x && y)
    {
        // Because computers count from zero, there's always
        // a one-element off-set unless you add lots of 0s to
        // the array:
        return multiply[x-1][y-1];
    }
    // so zero miltiplied by anything is always zero
    else
        return 0;
}
// Donkeysoft MMXII