求教！加入循环后出现逻辑错误

main()
{
      int day,month,year,sum,leap;
      
      loop :
     
      printf(“请输入年，月，日，如1986，4，21\n”);
     
      scanf(“%d,%d,%d”,&year,&month,&day);
     
      if(year>=0)
      {
                 if(month>0&&month<13)
                 {
                                      if(month==1&&month==3&&month==5&&month==7&&month==8&&month==10&&month==12)
                                      {if(day>32)
                                          {printf(“号数错误，请检查后重新输入\n”);
                                          goto loop;}
                                          }
                                      
                                      else if(month=2)
                                      {if(day>29)
                                          {printf(“号数错误，请检查后重新输入\n”);
                                          goto loop;}
                                          }
                                      else if(month==4&&month==6&&month==9&&month==11)
                                      {if(day>30)
                                          {printf(“号数错误，请检查后重新输入\n”);
                                          goto loop;}
                                          }
                 }
                 else{
                      printf(“月数输入错误，请检查后重新输入\n”);
                      goto loop;
                      }
                      }
      else
      {
           printf(“年数输入错误，请检查后重新输入\n”);
           goto loop;
           }
                            
     
      switch(month)
     
      {
                   case 1 : sum=0;  break;
                   case 2 : sum=31; break;
                   case 3 : sum=59; break;
                   case 4 : sum=90; break;
                   case 5 : sum=120;break;
                   case 6 : sum=151;break;
                   case 7 : sum=181;break;
                   case 8 : sum=212;break;
                   case 9 : sum=243;break;
                   case 10: sum=273;break;
                   case 11: sum=304;break;
                   case 12: sum=334;break;
                  
                   }
     
      sum=sum+day;
     
      if(year%400==0||(year%4==0&&year%100!=0))
          leap=1;
         
      else
          leap=0;
         
      if(leap=1&&month>2)
          sum++;
         
      printf(“是%d年中的第%d天\n”,year,sum);
     
      system(“pause”);
      }