Find the sum of an entire matrix using functions (C++) - c++

Question

I am writing some code that writes a matrix with a 10x10 size and prints it using functions. What I need is a function that takes the sum of the entire matrix array. What I have done is that I tried to sum up each row and column separately and add the total together. The problem with mine is that I believe that it only prints out the sum of the row or the column.
This is the code I have:
#include <iostream>
#include <ctime>
#include <iomanip>
#include <cstdlib>
using namespace std;
const int ROW_SIZE = 10;
const int COLUMN_SIZE = 10;
void initialize(int [][10], int, int);
void display(int matrix[][10], int, int);
void sum(int matrix[][COLUMN_SIZE], int, int);
int main() {
int matrix [ROW_SIZE][COLUMN_SIZE];
initialize(matrix, ROW_SIZE, COLUMN_SIZE);
display(matrix, ROW_SIZE,COLUMN_SIZE);
sum(matrix, ROW_SIZE,COLUMN_SIZE);
return 0;
}
void initialize(int matrix[][COLUMN_SIZE], int ROW_SIZE, int COLUMN_SIZE){
for (int i = 0; i < ROW_SIZE; i++){
for(int j = 0; j < COLUMN_SIZE; j++){
matrix[i][j] = 1 + rand() % 99;
}
}
}
void display(int matrix[][COLUMN_SIZE], int ROW_SIZE, int COLUMN_SIZE){
for(int i = 0; i < ROW_SIZE; i++){
for(int j = 0; j < COLUMN_SIZE; j++){
cout<< setw(4)<<matrix[i][j]<< " ";
}
cout<< endl;
}
}
void sum(int matrix[][COLUMN_SIZE], int ROW_SIZE, int COLUMN_SIZE){
int sum_row;
int sum_col;
for(int i = 0; i < ROW_SIZE; i++){
int sum_row = 0;
for(int j = 0; j < COLUMN_SIZE; j++){
sum_row = sum_row + matrix[i][j];
}
}
for(int i = 0; i < ROW_SIZE; i++){
int sum_col = 0;
for(int j = 0; j < COLUMN_SIZE; j++){
sum_col = sum_col + matrix[i][j];
}
}
int sum = sum_row + sum_col;
cout<<"The sum of the matrix is "<<sum<< endl;
}

Answer 1

What you have done is sum of last row + last column. This should be enough:
void sum(int matrix[][COLUMN_SIZE], int ROW_SIZE, int COLUMN_SIZE){
int sum = 0;
for(int i = 0; i < ROW_SIZE; i++){
for(int j = 0; j < COLUMN_SIZE; j++){
sum += matrix[i][j];
}
}
cout<<"The sum of the matrix is "<<sum<< endl;
}

Answer 2

few early problems in your code
void sum(int matrix[][COLUMN_SIZE], int ROW_SIZE, int COLUMN_SIZE){
int sum_row; // uninitialized make it equal to 0
int sum_col; // uninitialized make it equal to 0
for(int i = 0; i < ROW_SIZE; i++){
int sum_row = 0; // This is local to block and masks the sum_row above
for(int j = 0; j < COLUMN_SIZE; j++){
sum_row = sum_row + matrix[i][j];
}
}
for(int i = 0; i < ROW_SIZE; i++){
int sum_col = 0;
for(int j = 0; j < COLUMN_SIZE; j++){
sum_col = sum_col + matrix[i][j]; //Iterating over rows again matrix[j][i] may be
}
}
int sum = sum_row + sum_col;
cout<<"The sum of the matrix is "<<sum<< endl;
}
void sum(int matrix[][COLUMN_SIZE], int ROW_SIZE, int COLUMN_SIZE){
int sum_row = 0;
int sum_col = 0;
for(int i = 0; i < ROW_SIZE; i++)
for(int j = 0; j < COLUMN_SIZE; j++)
sum_row += matrix[i][j];
for(int i = 0; i < ROW_SIZE; i++)
for(int j = 0; j < COLUMN_SIZE; j++)
sum_col += matrix[j][i];
int sum = sum_row + sum_col;
cout<<"The sum of the matrix is "<<sum<< endl;
}
Now of course the question and logic doesn't seem to co-exist together and if sum of entire matrix means sum of all elements which is what it sounds like it can be achieved with the one here
void sum(int matrix[][COLUMN_SIZE], int ROW_SIZE, int COLUMN_SIZE){
int sum = 0;
for(int i = 0; i < ROW_SIZE; i++){
for(int j = 0; j < COLUMN_SIZE; j++){
sum += matrix[i][j];
}
}
cout<<"The sum of the matrix is "<<sum<< endl;
}

Answer 3

You're doing something wrong in terms of naming. You have constants called ROW_SIZE and COLUMN_SIZE and then you have parameters with the same names to functions like sum(). This is confusing for something reading your code. Call your parameters something else, like rows and columns.
Here is an alternative to the proposed solutions using std::accumulate().
const int ROW_SIZE = 3;
const int COLUMN_SIZE = 3;
void sum(int matrix[][COLUMN_SIZE], int const rows, int const cols)
{
int sum = std::accumulate(&matrix[0][0], &matrix[rows-1][cols], 0);
std::cout<<"The sum of the matrix is "<<sum<< std::endl;
}
int main()
{
int m[ROW_SIZE][COLUMN_SIZE] {{1,2,3}, {4,5,6}, {7,8,9}};
sum(m, ROW_SIZE, COLUMN_SIZE);
}
std::accumulate() takes the iterators that delimit a range. Those are the iterators to the first element and the one past the last element of the range. In this case, these are &matrix[0][0] and &matrix[row-1][col] (since &matrix[row-1][col-1] is the last element of the matrix). There are other ways to put that, such as the following:
auto begin = std::begin(matrix[0]);
int sum = std::accumulate(begin, begin + rows * cols, 0);