Diagonal sum

PROBLEM :

Given a square matrix of size M×M . Your task is to calculate the sum of its diagonals.

Input:
The first line of input contains an integer T denoting the number of test cases. Then T test cases follow. First line of each test case contains a single integer M denoting the size of the square matrix. The next  line contains M*M space separated values of the matrix A.

Output:
For each test case in a new line print the sum of diagonals of the matrix.

Constraints:
1 = T = 20
2 = N = 10
1 = A[i] = 20

Example:

Input:

1
3
1 1 1 1 1 1 1 1 1

Output:
6

--------------------------------------------------------------------------------
SIMPLE c++ IMPLEMENTATION :
--------------------------------------------------------------------------------

#include<iostream>
using namespace std;
#define MAX 10
int sum_matrix(int [MAX][MAX],int ) ;
int main()
 {
int t,no,mat[MAX][MAX] ;
int i,j ;
cin>>t ;
while(t--)
{
   cin>>no ;
   for(i=0;i<no;i++)
       for(j=0;j<no;j++)
           cin>>mat[i][j] ;
         
   cout<<sum_matrix(mat,no)<<endl ;
}
return 0;
}

int sum_matrix(int mat[MAX][MAX],int no)
{
    int i,j,sum ;
    sum=0 ;
   
    for(i=0;i<no;i++)
    {
        for(j=0;j<no;j++)
        {
            if(i==j)
                sum=sum+mat[i][j] ;
            if(i+j==no-1)
                sum=sum+mat[i][j] ;
        }
    }
    return sum ;
}

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