图的最小生成树prim算法

#include "stdio.h"
#include "stdlib.h"

//顶点数最大为99
#define max_size 99
//定义全局变量G
struct graph
{
 int matrix[max_size][max_size] ; //邻接矩阵
 int vnum ; //顶点数
} G ;

void prim(int r)
{
 int i , j , k;
 int min_i , min_j , min_value , sum = 0 ;

 G.matrix[r][r] = -1 ;
 for(k=1;k<G.vnum;k++)
 {
  min_value = (unsigned int)(-1)>>1 ;
  for(i=0;i<G.vnum;i++) 
   for(j=0;j<G.vnum;j++)
    if((G.matrix[i][i]+G.matrix[j][j])==-1&&G.matrix[i][j]>0&&G.matrix[i][j]<min_value)
    {
     min_value = G.matrix[i][j] ;
     min_i = i ;
     min_j = j ;
    }
  if(min_value == (unsigned int)(-1)>>1)