#include "stdio.h"
#include "time.h"
int main(void)
{
int i,a[1000],b,j,c;
printf("output the integers(1-10000):\n");
srand((unsigned)time(NULL));
for(i=0;i<1000;i++)
 {
a[i]=1+rand()%10000;
printf("%d ",a[i]);
 }
putchar('\n');
return 0;
b=a[0];
printf("%d ",a[0]);
j=0;
for(i=0;i<=998;i++)
{j=j+1;
for(;j<=999;j=j+1)
{if(b>a[j])
{b=a[j];
c=j;}
}
if(b>a[i])
a[i]=b;
a[j]=a[i];
}
for(i=0;i<=999;i++)
printf("%d ",a[i]);
getchar();
}

#include "stdio.h"
#include "time.h"
int main(void)
{
    int i, a[1000], b, j, c;
    printf("output the integers(1-10000):\n");
    srand((unsigned)time(NULL));
    for(i = 0; i < 1000; i++)
    {
        a[i] = 1 + rand() % 10000;
        //printf("%d ", a[i]);
    }
    printf("\n");
    //return 0;
    
    for(i = 0; i < 1000; i++)
    {   
        for(j = 0; j <1000; j++)
        {   if(a[i] > a[j])
            {   b = a[i];
                a[i] = a[j];
                a[j] = b;
            }
        }        
    }
    for(i = 0; i <1000; i++)
        printf("%d ", a[i]);
    getchar();
}

你的排序不对。

for(i = 0; i < 999; i++)
    {   
        c=i;
        for(j = i+1; j <1000; j++)
           if(a[c] > a[j])
                c=j;
         b = a[i];
         a[i] = a[c];
         a[c] = b;
                     
    }
这段排序供参考