【数据结构与算法】输入年、月、日，输出该日是该年第几天

#include <stdio.h>
#include <string.h>
int year,month,day,leap=0,sum=0;
int main(){
  int leaper(int year);
  int summer(int month,int day,int leap);
  printf("请输入年、月、日,用空格分隔:\n");
  scanf("%d %d %d",&year,&month,&day);
  int leap=leaper(year);
  if(!leap){
    if(month==2&&day>=29){
      printf("输入错误！\n");
      return 0;
    }
  }
  printf("该日是%d年的第%d天\n", year,summer(month,day,leap));
  return 0;
}
int leaper(int year){//判断闰年
  if(year%4==0&&year%100!=0){//闰年
    leap=1;
    return leap;
  }else if(year%400==0){//闰年
    leap=1;
    return leap;
  }else{//非闰年
    return leap;
  }
}
int summer(int month,int day,int leap){
  int b[12]={31,28,31,30,31,30,31,31,30,31,30,31};//月份数组
  int sum=0,i;
  if(day>b[month-1]){
    printf("error!\n");
    return 0;1
  }
  if(month==1){
    sum=day;
    return sum;
  }else {
    for(i=0;i<month-1;i++)
      sum+=b[i];
      if(leap&&month>2)
        sum+=1;
    return sum+day;
  }
}