判断某年某月某日是这一年第几天

Question

判断某年某月某日是这一年的第几天 程序未报错 不知道为什么结果一直不对

#include <iostream>
using namespace std;
/* run this program using the console pauser or add your own getch, system("pause") or input loop */

int main(int argc, char** argv) {
    int year,month,day,a,b,c,d;
    a==0;
    b==0;
    c==0;
    d==0;
    a==(month-1)*31+day+29;
    b==(month-1)*30+day+29;
    c==day;
    d==31+day;
    cout<<"Input year,month,day: "<<endl;
    cin>>year>>month>>day;
    if(year%4==0&&year%100!=0||year%100==0)
      switch(month){
      case 1:
      cout<<"Days of year: "<<c;
      break;
      case 3:
      case 5:
      case 7:
      case 8:
      case 10:
      case 12:
      cout<<"Days of year: "<<a;
      break;
      case 4:
      case 6:
      case 9:
      case 11:
      cout<<"Days of year: "<<b;
      break;
      case 2:
      cout<<"Days of year: "<<d;
      break;
      }
      else 
          switch(month)
          {
              case 1:
      cout<<"Days of year: "<<c;
      break;
      case 3:
      case 5:
      case 7:
      case 8:
      case 10:
      case 12:
      cout<<"Days of year: "<<a-1;
      break;
      case 4:
      case 6:
      case 9:
      case 11:
      cout<<"Days of year: "<<b-1;
      break;
      case 2:
      cout<<"Days of year: "<<d;
      break;
}
      return 0;
}

Answer 1

先输入再计算，赋值用一个=，不是两个

#include <iostream>
using namespace std;
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
 
int main(int argc, char** argv) {
    int year,month,day,a,b,c,d;
    a=0;
    b=0;
    c=0;
    d=0;
  
    cout<<"Input year,month,day: "<<endl;
    cin>>year>>month>>day;
    a=(month-1)*31+day+29;
    b=(month-1)*30+day+29;
    c=day;
    d=31+day;
    if(year%4==0&&year%100!=0||year%100==0)
      switch(month){
      case 1:
      cout<<"Days of year: "<<c;
      break;
      case 3:
      case 5:
      case 7:
      case 8:
      case 10:
      case 12:
      cout<<"Days of year: "<<a;
      break;
      case 4:
      case 6:
      case 9:
      case 11:
      cout<<"Days of year: "<<b;
      break;
      case 2:
      cout<<"Days of year: "<<d;
      break;
      }
      else 
          switch(month)
          {
              case 1:
      cout<<"Days of year: "<<c;
      break;
      case 3:
      case 5:
      case 7:
      case 8:
      case 10:
      case 12:
      cout<<"Days of year: "<<a-1;
      break;
      case 4:
      case 6:
      case 9:
      case 11:
      cout<<"Days of year: "<<b-1;
      break;
      case 2:
      cout<<"Days of year: "<<d;
      break;
}
      return 0;
}