This program matches the X and Y co-ordinate of the matrix and
calculates the sum where the co-ordinates match.Each and every element
of the matrix is considered using two for loops.The first for loop
considers row of the matrix and second for loop considers column
of the matrix.The variable sum stores the sum of diagonal elements.The
element whose row number matches with column number is called as
**diagonal element**.Such elements are added to variable sum
which gives the sum of diagonal elements when both the for loops
end.

#include < stdio.h > #include < conio.h > void main() { int a[10][10],i,j,sum=0,r,c; clrscr(); printf("\n Enter the number of rows and column "); scanf("%d%d",&r,&c); printf("\nEnter the %dX%d matrix",r,c); for(i=0;i < r;i++) { for(j=0;j < c;j++) { scanf("%d",&a[i][j]); }//for }//for for(i=0;i < r;i++) { for(j=0;j < c;j++) { if(i==j) { sum+=a[i][j]; } }//for }//for printf("\nThe sum of diagonal elements is %d",sum); }//main