Sales Force (sample solution)

Other answers are possible.

// constants
#define ITEMS 4
#define DAYS 7

// includes
#include <stdio.h>

// global arrays
int sales[DAYS][ITEMS] = {{7, 5, 26, 2},
                          {8, 2, 13, 1},
                          {6, 4, 22, 0},
                          {5, 7, 19, 0},
                          {6, 5,  8, 1},
                          {8, 4, 24, 3},
                          {9, 2, 43, 1}};

float prices[ITEMS] = {19.95, 14.95, 1.49, 65.59};

int main(void)
{
    // initial sales start as zero
    float weekly_total = 0.00;

    // arrays to hold daily and item totals
    float daily_totals[DAYS];
    float item_totals[ITEMS];

    // iterate over every items in sales
    for (int i = 0; i < DAYS; i++)
    {
        for (int j = 0; j < ITEMS; j++)
        {
            // calculate the daily sales amount
            float daily = sales[i][j] * prices[j];

            // add that amount to each set of totals, as appropriate
            daily_totals[i] += daily;
            weekly_total += daily;
            item_totals[j] += daily;
        }
    }

    // print the weekly total
    printf("%.2f\n\n", weekly_total);

    // print the seven daily totals
    for (int i = 0; i < DAYS; i++)
    {
        printf("%.2f\n", daily_totals[i]);

        // print an extra new line after the final daily
        if(i == DAYS - 1)
        {
            printf("\n");
        }
    }

    // print the four item totals
    for (int j = 0; j < ITEMS; j++)
    {
        printf("%.2f\n", item_totals[j]);
    }

    // all done!
    return 0;
}