C :

#include<stdio.h> 

main()
{
	int a[3][3];
	int i,j,b,c;
	b=0;c=0; 
	for(i=0;i<3;i++) for(j=0;j<3;j++) 
	{
		scanf("%d",&a[i][j]);
		if(i==j)b+=a[i][j]; 
		if(i+j==2)c+=a[i][j];
	}
	printf("%d\n",b);

}

C++ :

# include<stdio.h>
int main()
{
  int a[3][3];
  int i,j,n;
  for(i=0;i<=2;i++)
  {
	  for(j=0;j<=2;j++)
		  scanf("%d",&a[i][j]);
  }
  n=a[0][0]+a[1][1]+a[2][2];
  printf("%d\n",n);
 
}

Pascal :

program xzy1;
  var
    i,j,b:integer;
    a:array[1..3,1..3] of integer;
  begin
    for i:= 1 to 3 do
      for j:= 1 to 3 do
        read(a[i,j]);
      b:=a[1,1]+a[2,2]+a[3,3];
    writeln(b);
  end.