finding largest column

[petertohen]

For the array created I'm having a problem finding the largest column.

   #include<iostream>
using namespace std;
int main()
{
    int a[3][4];
    int i,j,s=0,sum=0;
    srand(((unsigned)time(0)));
    cout<<"Enter 9 elements of 3*4 Matrix \n";
    for(i=0;i<3;i++)
        for(j=0;j<4;j++)
            a[i][j] = 1 + rand() % 10;
    
    cout<<"Matrix Entered By you is \n";
    for(i=0;i<3;i++)
    {for(j=0;j<4;j++)
        cout<<a[i][j]<<" ";
        cout<<endl;
    }
    
    for(i=0;i<3;i++)
    {for(j=0;j<4;j++)
        s=s+a[i][j];
        cout<<"sum of"<<i+1<<" Row is"<<s;
        s=0;
        cout<<endl;
    }
    cout<<endl;
    for(i=0;i<4;i++)
    {for(j=0;j<3;j++)
        s=s+a[j][i];
        cout<<"sum of"<<i+1<<" Column is"<<s;
        s=0;
        cout<<endl;
    }
    
    cout<<endl;
    
    for(i=0;i<3;i++)
    for(j=0;j<4;j++)
        sum=sum+a[i][j];
        cout<<"Total Sum is "<<sum << endl;
    
    int largestSum = 0;
    for (int i = 0; i<3; i++)
    {
        int sum = 0;
        for (int j = 0; j<4; j++)
        {
            sum += a[i][j];
        }

        if (sum > largestSum)
        {
            largestSum = sum;
        }
    }
    cout << "largest row: " << largestSum << '\n';
    
    int largestColumn = 0;
    for (int i = 0; i<4; i++)
    {
        int sum = 0;
        for (int j = 0; j<3; j++)
        {
            sum += a[j][j];
        }
        
        if (sum > largestColumn)
        {
            largestColumn = sum;
        }
    }
    cout << "largest column: " << largestColumn << '\n';
}

http://www.cplusplus.com/doc/tutorial/

[lastchance]

Line 65:
sum += a[j][j];
should be
sum += a[j][i];
(i.e. indices are j, then i, not two lots of j)

You have made life staggeringly difficult for yourself (and anybody reading your code) by continually flipping the role of i and j indices. This is one place where using row and col (or r and c) might make for more clarity than using the common counting variables i and j.