C :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#define INF 1000000000

double G[110][110];
int axis[110][2];
int vis[110];
double d[110];
int n, m;
int A, B;

void dijkstra(){
memset(vis,0,sizeof(vis));
for(int i = 0;i <= n; i++)d[i] = INF;
d[A] = 0;
for(int i = 1;i <= n; i++){
    int u = -1, MIN = INF;
    for(int j = 1;j <= n; j++){
        if(vis[j]==0 && MIN > d[j]){
            u = j;
            MIN = d[j];
        }
    }
    if(u == B)return;
    vis[u] = 1;
    for(int v = 1;v <= n; v++){
        if(vis[v]==0 && G[u][v] != 0 && d[v] > d[u] + G[u][v]){
            d[v] = d[u] + G[u][v];
        }
    }
}
}

int main()
{
    while(scanf("%d",&n) != EOF){
        memset(G,0,sizeof(G));
        for(int i = 1;i <= n; i++){
            scanf("%d%d",&axis[i][0],&axis[i][1]);
        }
        scanf("%d",&m);
        while(m--){
            int a, b;
            scanf("%d%d",&a,&b);
            double dis = sqrt((axis[a][0]-axis[b][0])*(axis[a][0]-axis[b][0]) + \
                              (axis[a][1]-axis[b][1])*(axis[a][1]-axis[b][1]));
            G[a][b] = G[b][a] = dis;
        }
        scanf("%d%d",&A,&B);
        dijkstra();
        printf("%.2f\n",d[B]);
    }
    return 0;
}

C++ :

#include<cstdio>
#include<iostream>
#include<cstring>
#include<cmath>
using namespace std;
double x[110],y[110],dis[101],a[101][101];
bool v[101];
int n,m,xx,yy,st,ed;
int q[10000];
inline double calc(int i,int j){
	return sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));
}
void spfa(){
	memset(v,0,sizeof(v));
	for(int i=1;i<=n;++i) dis[i]=99999999.0;
	int l=1,r=1;
	q[1]=st;
	dis[st]=0;
	v[st]=true;
	while (l<=r){
		int x=q[l++];
		v[x]=false;
		for(int i=1;i<=n;++i)
		if (i!=x && a[x][i]<0x7fffffff)
			if (dis[i]>dis[x]+a[x][i]){
				dis[i]=dis[x]+a[x][i];
				if (!v[i]){
					v[i]=true;
					q[++r]=i;
				}
			}

	}
}
int main(){
	cin>>n;
	for(int i=1;i<=n;++i)
	  for(int j=1;j<=n;++j) a[i][j]=0x7fffffff;
	for(int i=1;i<=n;++i) a[i][i]=0;
	for(int i=1;i<=n;++i) scanf("%lf%lf",&x[i],&y[i]);
	cin>>m;
	for(int i=1;i<=m;++i){
		scanf("%d%d",&xx,&yy);
		if (xx!=yy)
			a[xx][yy]=a[yy][xx]=calc(xx,yy);
	}
	cin>>st>>ed;
	spfa();
	printf("%0.2lf",dis[ed]);
	return 0;
}

Pascal :

program spfa;
  type
    point=^node;
    node=record
      y:longint;
      z:real;
      next:point;
    end;

    jj=record
      x,y:longint;
    end;

  var
    i,j,n,m,s,t,x,y:longint;
    dist:array[0..100] of real;
    v:array[0..100] of boolean;
    a:array[0..100] of point;
    b:array[0..100] of jj;
    q:array[0..1000000] of longint;

  procedure insert;
    var
      p:point;
    begin
      new(p); p^.y:=y; p^.z:=sqrt(sqr(b[x].x-b[y].x)+sqr(b[x].y-b[y].y)); p^.next:=a[x]; a[x]:=p;
      new(p); p^.y:=x; p^.z:=sqrt(sqr(b[x].x-b[y].x)+sqr(b[x].y-b[y].y)); p^.next:=a[y]; a[y]:=p;
    end;

  procedure spfa;
    var
      head,tail,x,y:longint;
      z:real;
      p:point;
    begin
      head:=0; tail:=1; q[1]:=s; v[s]:=true; dist[s]:=0;
      while head<tail do
        begin
          inc(head);
          x:=q[head];
          p:=a[x];
          while p<>nil do
            begin
              y:=p^.y;
              z:=p^.z;
              if dist[y]>dist[x]+z then
                begin
                  dist[y]:=dist[x]+z;
                  if not v[y] then
                    begin
                      v[y]:=true;
                      inc(tail);
                      q[tail]:=y;
                    end;
                end;
              p:=p^.next;
            end;
            v[x]:=false;
        end;
    end;

  begin

    readln(n);
    for i:=1 to n do
      readln(b[i].x,b[i].y);
    readln(m);
    for i:=1 to n do
      dist[i]:=9999999;
    for i:=1 to m do
      begin
        readln(x,y);
        insert;
      end;
    readln(s,t);
    spfa;
    writeln(dist[t]:0:2);

  end.