各位大侠帮帮忙！小弟编了一个数组乱序排列的程序，可是结果却不对！请问错在哪里？
#include <iostream>
#include <time.h>
#include <iomanip>
using namespace std;
int main()
{
    int k,a,b,i,j,t;
    int pake[4][12];
    for (i=0;i<4;i++)
        for(j=0;j<12;j++)
            pake[i][j]=j+1;         //输入
    for(k=0;k<10000;k++)
    {
        srand( (unsigned)time( NULL ) );
        i=rand()%3;
        j=rand()%11;
        a=rand()%3;
        b=rand()%11;
        t=pake[i][j];
        pake[i][j]=pake[a][b];
        pake[i][j]=t;
    }                             //洗牌
   

    for (i=0;i<4;i++)
        for(j=0;j<12;j++)
       cout<<setw(3)<<pake[i][j];
    return 0;
}