求两日期之间的相隔天数（year，month，day） C语言代码

    #include<cstdio>  
    int isRunNian(int year);  
    int DiJiTian(int year,int month,int day);  
    void swap(int *a,int *b);  
    int main()  
    {  
        int year1,month1,day1;  
        int year2,month2,day2;  
        int sum=0;  
        scanf("%d%d%d",&year1,&month1,&day1);  
        scanf("%d%d%d",&year2,&month2,&day2);  
        if(year1==year2)  
        {  
            sum = DiJiTian(year1,day1) - DiJiTian(year2,day2);   
            if(sum<0)  
                sum=-sum;  
        }  
        else  
        {  
            if(year1 > year2)  
            {  
                swap(&year1,&year2);  
                swap(&month1,&month2);  
                swap(&day1,&day2);  
            }  
            int a,b,c;  
            if(isRunNian(year1))  
                a=366-DiJiTian(year1,day1);  
            else  
                a=365-DiJiTian(year1,day1);  
              
            b=0;  
            int i;  
            for(i=year1+1;i<year2;i++)  
            {  
                if(isRunNian(i))  
                    b+=366;  
                else  
                    b+=365;  
            }  
              
            c=DiJiTian(year2,day2);  
              
            sum=a+b+c;  
        }  
          
        printf("%dn",sum);  
        return 0;  
    }  
      
      
      
    /*判断闰年的函数*/  
    int isRunNian(int year)  
    {  
        if(year%400==0||(year%4==0&&year%100!=0))  
            return 1;  
        else  
            return 0;  
    }   
      
    /*判断这一天是这一年的第几天函数*/  
    int DiJiTian(int year,int day)  
    {  
        int i,sum=0;  
        for(i=1;i<month;i++)//step1  
        {  
            if(i==1||i==3||i==5||i==7||i==8||i==10||i==12)  
                sum+=31;  
            else if(i==4||i==6||i==9||i==11)  
                sum+=30;  
            else if(i==2)  
            {  
                if(isRunNian(year))  
                    sum+=29;  
                else  
                    sum+=28;  
            }  
        }  
        sum+=day;//step2  
        return sum;//step3  
    }  
      
    /* 交换两个变量的值的函数 */  
    void swap(int *a,int *b)  
    {  
        int c;  
        c=*a;  
        *a=*b;  
        *b=c;  
    }