Time Calculation

main.c

//  Created by Vanessa Leung on 2019/2/22.

#include <stdio.h>
#include <string.h>

//Declare all functions to be used first

//isLeapYear
int leap(int year){
    if (((year % 400 == 0) && (year % 3200 != 0)) ||
        ((year % 4 == 0) && (year % 100 != 0)))
        return 1;
    else
        return 0;
}

//Days in month
int numdays(int month){
    if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12)
        return 31;
    else if (month == 2)
        return 28;
    else
        return 30;
}

//main function
int main()
{
    //Loop for continued input
    while(1){
        int valid = 0;
        int year = 0, month = 0, day = 0, hour = 0, minute = 0;
        int duration, hold, numday = 0;
        
        //Check if date is valid
        while (valid == 0){
            char date[255], Year[255], Month[255], Day[255], Hour[255], Minute[255];
            
            //Read Date as string
            printf("Enter Origin Date: (e.g. 201901010900)\n");
            scanf("%s", date);
            //Assign year, month, day, hour
            strncpy(Year, date, 4);
            strncpy(Month, date + 4, 2);
            strncpy(Day, date + 6, 2);
            strncpy(Hour, date + 8, 2);
            strncpy(Minute, date + 10, 2);
            //Convert string to integer
            sscanf(Year, "%d", &year);
            sscanf(Month, "%d", &month);
            sscanf(Day, "%d", &day);
            sscanf(Hour, "%d", &hour);
            sscanf(Minute, "%d", &minute);
            
            //Calculate number of days in month
            if ((leap(year) == 1) && (month == 2)){     //Special case: February in leap years
                numday = 29;
            } else{
                numday = numdays(month);
            }
            //If input is invalid
            if ((month > 12) || (day > numday) || (hour >= 24) || (minute >= 60)){
                printf("Please Enter a Valid Date!\n");
            } else{
                valid = 1;
            }
        }
        
        //Read Duration
        printf("Enter Duration: (in minutes)\n");
        scanf("%d", &duration);
        
        //Make a copy to avoid any modification on original data
        int year2 = year, month2 = month, day2 = day, hour2 = hour, minute2 = minute;
        
        //If duration >= 60mins, then hour++
    
        hour2 += duration / 60;
        hold = duration % 60;
    
        //If minute >= 60mins, then hour++
        if (hold + minute >= 60){
            minute2 += hold - 60;
            hour2 ++;
        } else{
            minute2 += hold;
        }
    
        //If hour >= 24hrs, then day++
        if (hour2 >= 24){
            day2 += hour2 / 24;
            hour2 = hour2 % 24;
        }
    
        //If day > days in month, then month++
        if (day2 > numday){
            //Update numday & month2 till day2 < numday(month2)
            while (day2 > numday){
                month2 ++;
                if (month2 > 12){
                    year2 ++;
                    month2 -= 12;
                }
                day2 -= numday;
                numday = numdays(month2);
            }
        }
    
        //If month > 12, then year++
        if (month2 > 12){
            year2 += month2 / 12;
            month2 = month2 % 12;
        }
        
        
        printf("Original Time: %d/%d/%d %d:%d\n", year, month, day, hour, minute);
        printf("New Time:      %d/%d/%d %d:%d\n", year2, month2, day2, hour2, minute2);

        //Loop
        printf("Press [Enter] to continue.\n");
        while(getchar()!='\n');
        getchar();
    }
    return 0;
}