Question

How to find the sum of diagonals of a matrix in C++

Answer 1

#include <iostream>

#define COLS 5
  
int sumDiagonals(int matrix[][COLS], int rows, int cols) {
    int sumDiagonalLeft = 0, sumDiagonalRigth = 0;
  
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < COLS; j++) {
            if (i == j) {
                sumDiagonalLeft += matrix[i][j];
            }
            if ((i + j) == rows - 1) {
                sumDiagonalRigth += matrix[i][j];
            }
        }
    }
  
    std::cout << "sumDiagonalLeft = " << sumDiagonalLeft << 
                 " \nsumDiagonalRigth = " << sumDiagonalRigth << "\n";
  
    return sumDiagonalLeft + sumDiagonalRigth;
}
  
  
int main()
{
    int matrix[][COLS] = { { 1,   2,   3,   4,  0 },
                           { 5,   6, 100,   8,  1 },
                           { 2, 100,   8, 100,  3 },
                           { 1,   7, 100,   9,  6 },
                           { 9,  10,  11,  12, 13 } };
  
      
    // sumDiagonalLeft = (1 + 6 + 8 + 9 + 13) = 37
    // sumDiagonalRigth = (0 + 8 + 8 + 7 + 9) = 32 
  
    // 37 + 32 = 69
  
    int rows = sizeof matrix / sizeof matrix[0];
    int cols = sizeof matrix[0] / sizeof(int);
  
    std::cout << sumDiagonals(matrix, rows, cols);
}
  
  
  
  
/*
run:
  
sumDiagonalLeft = 37
sumDiagonalRigth = 32
69
  
*/

 

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Answer 2

#include <iostream>
  
#define COLS 5
    
int sumDiagonals(int matrix[][COLS], int rows, int cols) {
    int sumDiagonalLeft = 0, sumDiagonalRigth = 0;

    for (int i = 0; i < rows; i++){
        sumDiagonalLeft += matrix[i][i];
        sumDiagonalRigth += matrix[i][cols - i - 1];
    }
 
    
    std::cout << "sumDiagonalLeft = " << sumDiagonalLeft << "\n";
    std::cout << "sumDiagonalRigth = " << sumDiagonalRigth << "\n";
    
    return sumDiagonalLeft + sumDiagonalRigth;
}
    
    
int main()
{
    int matrix[][COLS] = { { 1,   2,   3,   4,  0 },
                           { 5,   6, 100,   8,  1 },
                           { 2, 100,   8, 100,  3 },
                           { 1,   7, 100,   9,  6 },
                           { 9,  10,  11,  12, 13 } };
    
        
    // sumDiagonalLeft = (1 + 6 + 8 + 9 + 13) = 37
    // sumDiagonalRigth = (0 + 8 + 8 + 7 + 9) = 32 
    
    // 37 + 32 = 69
    
    int rows = sizeof matrix / sizeof matrix[0];
    int cols = sizeof matrix[0] / sizeof(int);
    
    std::cout << sumDiagonals(matrix, rows, cols);
}
    
    
    
    
/*
run:
    
sumDiagonalLeft = 37
sumDiagonalRigth = 32
69
    
*/

 

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