PAT (Basic Level) Practice （中文）1019 数字黑洞

#include<stdio.h>

int fun1(char *str)
{
    int i,j;
    int index;
    char temp;
    int sum=0;
    for(i=0;i<4-1;i++)
    {
        index=i;
        temp=str[i];
        for(j=i+1;j<4;j++)
        {
            if(str[j]-'0'>=str[index]-'0') index=j;
        }
        str[i]=str[index];
        str[index]=temp;
    }
    for(i=0;i<4;i++)
    {
        printf("%c",str[i]);
        sum=sum*10+(str[i]-'0');
    }
    printf(" - ");
    return sum;
}

int fun2(char *str)
{
    int i,j;
    int index;
    char temp;
    int sum=0;
    for(i=0;i<4-1;i++)
    {
        index=i;
        temp=str[i];
        for(j=i+1;j<4;j++)
        {
            if(str[j]-'0'<=str[index]-'0') index=j;
        }
        str[i]=str[index];
        str[index]=temp;
    }
    for(i=0;i<4;i++)
    {
        printf("%c",str[i]);
        sum=sum*10+(str[i]-'0');
    }
    printf(" = ");
    return sum;
}

int fun3(int sum1,int sum2)
{
    int temp=sum1-sum2;
    if(temp>999) printf("%d\n",temp);
    if(temp>99&&temp<=999) printf("0%d\n",temp);
    if(temp>9&&temp<=99) printf("00%d\n",temp);
    if(temp>0&&temp<=9) printf("000%d\n",temp);
    if(temp==0) printf("0000\n");
    return temp;
}

void fun4(char *str,int n)
{
    int j=3;
    str[0]='0';
    str[1]='0';
    str[2]='0';
    str[3]='0';
    while(n)
    {
        str[j--]=(n%10)+'0';
        n/=10;
    }
}
int main()
{
    char str[50];
    str[0]='0';str[1]='0';str[2]='0';str[3]='0';
    char str1[50];
    gets(str1);
    int i;
    int len=strlen(str1);
    for(i=len-1;i>=0;i--)
    {
        str[3-i]=str1[i];
    }

    if(str[0]==str[1]&&str[1]==str[2]&&str[2]==str[3]) printf("%s - %s = 0000\n",str,str);
    else
    {
        while(1)
        {
            int sum1=fun1(str);
            int sum2=fun2(str);
            int temp=fun3(sum1,sum2);
            if(temp==6174) break;
            else
            {
               fun4(&str,temp);
            }
        }
    }
    return 0;
}