c - Days between dates will not compile -

i have been trying work. need input 2 dates (mm dd) , have program tell me amount of days between 2 dates. reason when try use month 2 (february) dont think registering indicated having 28 days. when enter same date cant "0". please thank you

#include <stdio.h> #include <stdlib.h>  //constructs dates calculation struct date{     int month;     int day; };//end date  int main() {     struct date first, second; //creates 2 dates calculate     int finaldays = 0;     int total = 0;     int = 0;     int valid=0;      printf("enter first date \n");     scanf("%d %d", &first.month, &first.day); //user input: first date     if (first.month == 1||3||5||7||8||10){        if(first.day > 31){         printf("invalid day\n");         valid += 1;        }     }     else if (first.month == 4||6||9||11 ){         if (first.day > 30){          printf("invalid day\n");          valid += 1;         }     }     else if (first.month == 2){         if(first.day > 28){          printf("invalid day");          valid += 1;         }     }      printf("enter second date\n");     scanf("%d %d", &second.month, &second.day); // user input: second date     if (second.month == 1||3||5||7||8||10){        if(second.day > 31){         printf("invalid day\n");         valid += 1;        }     }     else if (second.month == 4||6||9||11 ){         if (second.day > 30){          printf("invalid day\n");          valid += 1;         }     }     else if (second.month ==2){         if(second.day > 28){          printf("invalid day");          valid += 1;         }     }      if (first.month == second.month && first.day == second.day){         printf("days between dates: 0");         valid += 1;     }      //prints statement if month invalid     if(first.month > 12 || second.month > 12 || first.month<1 || second.month<1){         printf("invalid date: invalid month");     }      //prints statement if second date precedes first     if(second.month<first.month){         printf("invalid. second date cannot precede first date.");     }     if (second.month==first.month && second.day<first.day){         printf("invalid. second date cannot precede first date.");     }      if(first.month==second.month){         finaldays = (second.day - first.day);         printf("days between dates: %d", finaldays);         valid+=1;     }      if(first.month == 1||3||5||7||8||10||12)         // days remaining in first month         total = 31 - first.day;     else if(first.month == 4||6||9||11)         total = 30 - first.day;     else if(first.month == 2)         total = 28 - first.day;      for(i = first.month + 1; < second.month; i++)     {       if(i == 3||5||7||8||10||12)           total += 31;       else if(i == 4||6||9||11)           total += 30;     }     total += second.day;      if(valid == 0){     printf("first date: %d %d \n", first.month, first.day);     printf("second date: %d %d \n", second.month, second.day);     printf("days between dates: %d", total);     }      return 0; } //end main 

if (first.month == 1||3||5||7||8||10){ 

this won't want do. evaluated (first.month == 1)||3||5||7||8||10, evaluate true non-zero months.

this better written case statement;

switch (first.month) {     case 1:     case 3:     case 5:     case 7:     case 8:     case 10:         /* handle 31 day months */         ...         break;     case 4:     case 6:     case 9:     case 11:         /* handle 30 day months */         ...         break;     case 2:         /* handle february */         ...         break;     default:         /* handle invalid month */         break; }