C :

#include<stdio.h>
#define N 10
void InputMatrix(int a[N][N],int n);
int AddDiagonal(int a[N][N],int n);
int main()
{
	int a[N][N],n,sum;
	scanf("%d",&n);
	InputMatrix(a,n);
	sum=AddDiagonal(a,n);
	printf("%d",sum);
	return 0;
} 
void InputMatrix(int a[N][N],int n)
{
	int i,j;
	for(i=0;i<n;i++)
	{
		for(j=0;j<n;j++)
		{
			scanf("%d",&a[i][j]);
		}
	}
}
int AddDiagonal(int a[N][N],int n)
{
	int i,j,sum=0;
	for(i=0;i<n;i++)
	{
		for(j=0;j<n;j++)
		{
			if(i==j||i+j==n-1)
			    sum=sum+a[i][j];
		}
	}
	return sum;
}

Pascal :

program p23283;

 var
 n,i,j,s:longint;
 a: array[1..100,1..100] of longint;

 begin
 readln(n);
 for i:=1 to n do
  for j:=1 to n do
   read(a[i,j]);
 s:=0;
 for i:=1 to n do
  for j:=1 to n do
   if (i=j) or (i+j=n+1) then
    s:=s+a[i,j];
 writeln(s);
end.