16:19 ~/318 > cat fw.cpp
#include <iostream>
#include <iomanip>

int smin(int a, int b)
{ if (a == -1) return b;
  if (b == -1) return a;
  if (a < b) return a;
  return b; }

int splus(int a, int b)
{ if (a == -1) return -1;
  if (b == -1) return -1;
  return a + b; }

typedef int mat5[5][5];

void step(int i, mat5 prev, mat5 next)
{ for (int r = 0; r < 5; r += 1)
    for (int c = 0; c < 5; c += 1)
      next[r][c] = smin(prev[r][c], 
                        splus(prev[r][i], prev[i][c])); }

void display(int i, mat5 di)
{ cout << "D" << i << ":\n";
  for (int r = 0; r < 5; r += 1)
  { for (int c = 0; c < 5; c += 1)
      cout << setw(3) << di[r][c];
    cout << "\n"; }
  cout << "\n\n"; }

int main()
{ mat5 d0 = { {  0,  1,  3, -1, -1 },
              {  1,  0,  1, -1,  7 },
              {  3,  1,  0,  1,  3 },
              { -1, -1,  1,  0,  1 },
              { -1,  7,  3,  1,  0 } };
  mat5 d1, d2, d3, d4, d5;

  step(0, d0, d1);
  step(1, d1, d2);
  step(2, d2, d3);
  step(3, d3, d4);
  step(4, d4, d5);

  display(0, d0);
  display(1, d1);
  display(2, d2);
  display(3, d3);
  display(4, d4);
  display(5, d5); }

16:19 ~/318 > CC fw.cpp
16:19 ~/318 > a.out
D0:
  0  1  3 -1 -1
  1  0  1 -1  7
  3  1  0  1  3
 -1 -1  1  0  1
 -1  7  3  1  0


D1:
  0  1  3 -1 -1
  1  0  1 -1  7
  3  1  0  1  3
 -1 -1  1  0  1
 -1  7  3  1  0


D2:
  0  1  2 -1  8
  1  0  1 -1  7
  2  1  0  1  3
 -1 -1  1  0  1
  8  7  3  1  0


D3:
  0  1  2  3  5
  1  0  1  2  4
  2  1  0  1  3
  3  2  1  0  1
  5  4  3  1  0


D4:
  0  1  2  3  4
  1  0  1  2  3
  2  1  0  1  2
  3  2  1  0  1
  4  3  2  1  0


D5:
  0  1  2  3  4
  1  0  1  2  3
  2  1  0  1  2
  3  2  1  0  1
  4  3  2  1  0