Matriz de 5x5...

main.cpp

#include <cstdlib>
#include <iostream>

using namespace std;

int main(int argc, char *argv[])
{
    int m[5][5] = {
        {1,2,3,4,5},
        {6,7,8,9,10},
        {11,12,13,14,15},
        {16,17,18,19,20},
        {21,22,23,24,25}
        };

    for (int i = 0; i < 5; i++) {
        for (int j = 0; j < 5; j++) {
            if (j == 4-i || j == i) {
                printf("%d",m[i][j]);
            } else {
                printf("0");
            }
            printf("\t");
        }
        printf("\n");
    }
    system("PAUSE");
    return EXIT_SUCCESS;
}