C++ :: How To Get Sum Of Rows And Columns In 2 Dimensional Array

Here's my code for adding the rows and columns. My problem is that my program displays an incorrect output.

main() {
int a[20][20],r,c,y,x,sum=0,rn,cn,cs=0,rs=0;
cout<<"Enter number of columns : ";
cin>>cn;

[Code] .....

This should be the output
Enter number of columns: 4
Enter number of rows: 3
Enter twelve numbers: 9 2 3 4 2 3 1 2 5 6 7 8

The numbers are:
9234
2312
5678
Sum of number 1 column is: 16
Sum of number 2 column is: 11
Sum of number 3 column is: 11
Sum of number 4 column is: 14
Sum of number 1 row is: 18
Sum of number 2 row is: 8
Sum of number 3 row is: 26