abs_diff of sum of diagonal elements of matrix

C - program:

#include<stdio.h>

#include<math.h>

#include<string.h>

int main()

{

int n,j;

int i=0,rds=0,lds=0,f,s;

scanf("%d",&n);

int a[n][n];

for(int f=0;f<n;f++)

{

for(s=0;s<n;s++)

{

scanf("%d",&a[f][s]);

}

while(i<n)

{

rds=rds+a[i][i];

i++;

}

j=n-1,i=0;

while(i<n)

{

lds=lds+a[i][j];

i++;

j--;

}

printf("%d",abs(rds-lds));

return 0;

}

Input : a[][] = 10 2
                   4 5
Output : 7

Input : a[][] = 11 2  4
                   4 5  6
                  10 8 -12 
Output : 15

Explanation
Sum of primary diagonal = 11 + 5 + (-12) = 4.
Sum of primary diagonal = 4 + 5 + 10 = 19.
Difference = |19 - 4| = 15.