products.c

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

unsigned intToBinaryInt(unsigned k, int *components, int counter) {
    // k            - current binary component
    // components   - collection of all the components
    // counter      - tracks how many components are there
    if (k == 0) {
        components[counter] = k;
        return 0;
    }
    if (k == 1) {
        components[counter] = k;
        return 1;
    }
    components[counter] = (k % 2);
    return (k % 2) + 10 * intToBinaryInt(k / 2, components, ++counter);
}

int multiply(int *components, int elements[], int elementCount) {
    // components   - marks each element from array to be multiplied by 1
    // elements     - the array that contains all the factors
    // elementCount - how many
    int i, j, product = 0;
    for (i = 0; i < elementCount; i++) {
        if (product)
            product *= (components[i] * elements[i]) > 0 ? (components[i] * elements[i]) : 1;
        else
            product += components[i] * elements[i];
    }
    return product;
}

int main() {
    // Storage
    int     elements        = 4,            // Numbers of factors
            small[4]        = {2, 5, 7, 8}, // Factors
            big[100]        = {0},          // Binary components
            multiples[100]  = {0};          // The array of all possible products

    // Counters
    int     loops           = pow(2, elements), // How many possible combinations
            counter         = 0;                // The number of the current one

    for (counter = 1; counter < loops; counter++) {
        // Find a new configuration of multiples
        intToBinaryInt(counter, big, 0);
        // Include it into the collection
        multiples[counter] = multiply(big, small, elements);
    }

    //
    // Print the collection of multiples
    //
    printf("{");
    for (counter = 1; counter < (loops-1); counter++) {
        printf("%d, ", multiples[counter]);
    }
    printf("%d}\n", multiples[++counter]);
}