程序代码：

#include<stdio.h>
int main(){
    int m,n,count;
    for(m=1000;m<=20000;m++){
        n=m;
        count=0;
        while(n){
            if(n%10==9)
               count++;
            n/=10;
        }
        if(count==3)
        printf("%d ",m);    
    }
}

程序代码：

#include <stdio.h>

int main( void )
{
    for( unsigned n=1000,index=0; n<=20000; ++n )
    {
        unsigned count = 0;
        for( unsigned t=n; t; t/=10 )
            if( t%10 == 9 )
                ++count;

        if( count == 3 )
            printf( "%u%c", n, " \n"[(++index)%8==0] );
    }
}