#include<stdio.h>
int main()
{
    int b[1000];
    int r,i,n,s,a;
    while(scanf("%d %d",&n,&r)!=EOF)
    {
        s=0;
        a=n;
        if(n<0)
            n=-n;
        for(i=0;n!=0;i++)
        {
            b[i]=n%r;
            s++;
            n=n/r;
        }
        if(r<10)
        {
            if(a<0)
            {
                printf("-");
                for(i=s-1;i>=0;i--)
                {
                    printf("%d",b[i]);
                }
            }
            else if(a>0)
            {
                for(i=s-1;i>=0;i--)
                {
                    printf("%d",b[i]);
                }
            }
        }
        else
        {
            for(i=s-1;i>=0;i--)
            {
                printf("%c",b[i]+64);//要让23 12的时候是1B，这里改怎么改？//
            }
        }
        printf("\n");
    }
    return 0;
}

printf("%c",b[i]+64); //可以这样改：  printf("%c",b[i]>=10?b[i]%10+65:b[i]+48);

好了，谢谢！