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Problem in 2D array

AliElsaid (2)
I was trying to create a program that calculates the sum of rows and columns in 2D array and the elements should be obtained from the user, when I tried to run the program the sum of the rows was a very large number even if the inputs were zeros
so please if you detected what's wrong inform me.

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  #include <iostream>
using namespace std;

int main(){
int r;
int c;
cout << "Enter the number of rows ";
cin >> r;
cout << "Enter the number of cols ";
cin >> c;
int a[r][c];
int sumr[r];
int sumc[c];
for (int i=0 ; i<r ; i++){
    for (int j=0 ; j<c ; j++){
        cin >> a[i][j];
         sumr[i] +=a[i][j];
         sumc[j] +=a[i][j];

    }
     cout << "The sum of row " << i+1 << " is " << sumr[i] << endl;

}

int y;


cout << "Enter the col no. to calc it's sum ";
cin >> y;
if (y>c || y<0){
    cout << "Invalid col input ";
    return 0;
}


cout << "The sum of col "<< y << " is " << sumc[y] << endl;


}
Last edited on
shadder (813)
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int sumr[r];
int sumc[c];


You have to initialize them to zero

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int sumr[r]=0;
int sumc[c]=0;


otherwise they will hold garbage value
Last edited on
JayhawkZombie (738)
int a[r][c];
We cannot do that.

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	int **arr = new int*[rows];
	for (int i = 0; i < rows; i++)
		arr[i] = new int[columns];

        //Do whatever

	for (int i = 0; i < rows; i++)
		delete[] arr[i];
	delete[] arr;


You should also initialize your array to hold all zeros after you create it (or as you create it)
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int **arr = new int*[rows];
for (int i = 0; i < rows; i++)
  arr[i] = new int*[columns] {0};
...


And you might want to check your row/col summing algorithm.
closed account (48T7M4Gy)
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#include <iostream>
using namespace std;

int main()
{
    int rows = 0;
    int cols = 0;
    
    cout << "Enter the number of rows ";
    cin >> rows;
    rows++; // <-- make 1 extra row for totals
    
    cout << "Enter the number of cols ";
    cin >> cols;
    cols++; // <-- ditto column
    
    int** a = new int*[rows];
    for(int i = 0; i < rows; ++i)
        a[i] = new int[cols];
    
    for (int i = 0 ; i < rows - 1 ; i++)
    {
        for (int j = 0 ; j < cols - 1 ; j++)
        {
            cin >> a[i][j];
            a[i][cols - 1] += a[i][j]; // <-- total as you go
            a[rows - 1][j] += a[i][j]; // <-- ditto
        }
    }
    
    int y;
    
    cout << "Enter the col no. to calc it's sum ";
    cin >> y;
    
    if ( y > cols || y < 0)
    {
        cout << "Invalid col input ";
        return 0;
    }
    cout << "The sum of col "<< y << " is " << a[rows - 1][y - 1] << endl;
    
    //delete cleanup required
}


http://stackoverflow.com/questions/936687/how-do-i-declare-a-2d-array-in-c-using-new

Another way but a little quick, dirty and sloppy, is to make a big array say a[100][100], initialize it to zero, and input the values of r and c to use as limiters/locators only. Easy to do and no need to use new/delete.
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