C++ random 2d array with average

Question

Can't get random numbers in range 1-100. The average is also wrong.

Any advice is greatly appreciated.
#include <iostream>

#include <cstdlib>

#include <ctime>

#include <cmath>

using namespace std;

int main()

{

   srand(time(NULL));

   const int rows = 3;

   const int cols = 3;

   double sum = 0;

   int grades[rows][cols];

   int row, col;

   for (int r = 0; r < rows; ++r) {

       row = rand() % 100 + 0;

       for (int c = 0; c < cols; ++c) {

           col = rand() % 100 + 0;

           grades[r][c] = (rand() % 100) + 0;

           sum += grades[r][c];

           cout << sum << " ";

       }

       double average =  sum / (rows + cols);

       cout << "Average: " << average<<endl;

       cout << endl;

   }

   return 0;

}

Answer 1

Variables row and col do not appear to be needed, so we can remove those. To generate a number between 1 and 100 (inclusive), you have to add 1 to rand() % 100, not 0.

Move double average = sum... till cout << endl out of the outer loop. Those are generated after you've completed all the iterations. Also, average should be sum/(rows*cols), not rows+cols.

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;

int main() {
   srand(time(NULL));
   const int rows = 3;
   const int cols = 3;
   double sum = 0;
   int grades[rows][cols];

   for (int r = 0; r < rows; ++r) {
       for (int c = 0; c < cols; ++c) {
           grades[r][c] = (rand() % 100) + 1;
           sum += grades[r][c];
        }
}
   double average =  sum / (rows * cols);
cout << "Average: " << average << endl;
 cout << endl;
   return 0;
}

Answer 2

thanks a lot Hasty Rei