c program time conversion 24-h to 12-h

Question

Is there anything wrong with my code? It's a program that coverts 24-h time format to 12-h time format, and only takes a four-digit integer as input.

ex. input = 0000 then output should be 00:00 a.m.

When I submit my code to schools online judge, it doesn't accept all inputs, but I can't find out the problem.

#include <stdio.h>

int main(void)
{
    int morning, hour, min;

    scanf("%02d%02d", &hour, &min);

    if (hour > 23 || min > 59)
    {
        return 1;
    }


    //check am pm
    if (hour >= 12)
    {
        morning = 1;

        if (hour > 12)
        {
            hour -= 12;
        }

    }
    else
    {
        morning = 0;
    }

    //print the result
    if (morning == 0)
    {
        printf("%02d:%02d a.m.", hour, min);
    }
    else
    {
        printf("%02d:%02d p.m.", hour, min);
    }

    return 0;
}

`00:00 am` is a valid time?? I would think it would be `12:00 am`. — Fred Larson, Sep 28 '18 at 15:46
You could look at [Convert 12-hour date/time to 24-hour?](https://stackoverflow.com/questions/440061/convert-12-hour-date-time-to-24-hour-date-time/) for some ideas and information. It covers the converse transformation, but many of the issues are the same. Remember, 11:59 am is almost 12 hours later than 12:01 am. — Jonathan Leffler, Sep 28 '18 at 16:01
Minor: the `0`s are not needed in `scanf("%02d%02d", &hour, &min);` — chux - Reinstate Monica, Sep 28 '18 at 16:09
You must check the result of `scanf`. If it is not 2, then the input was invalid. — Paul Ogilvie, Sep 28 '18 at 16:32
Thanks guys, I think I noticed my problem. It should be 12:00 instead of 00:00! — sky3691841, Sep 28 '18 at 16:33

Agui Navarro · Answer 1 · 2018-09-28T22:13:18.780

With your code, if the hour = 0 and min = x, the output with be 00:xx am. With 12 hour time, there is no 00:xx am. There is a 12:xx am, however. Therefore, you need to include another if statement if hour = 0.

#include <stdio.h>

int main(void)
{
    int morning, hour, min;

    scanf("%02d%02d", &hour, &min);

    if (hour > 23 || min > 59)
    {
        return 1;
    }


    //check am pm
    if (hour >= 12)
    {
        morning = 1;

        if (hour > 12)
        {
            hour -= 12;
        }

    }
    //if input is 00xx
    if (hour == 0)
    {
    morning = 2;
    hour = hour + 12;
    }
    else
    {
        morning = 0;
    }

    //print the result
    if (morning == 2); 
    {
    printf("%02d:%02d a.m.\n", hour, min);
    }   
    if (morning == 0)
    {
        printf("%02d:%02d a.m.\n", hour, min);
    }
    if (morning == 1)
    {
        printf("%02d:%02d p.m.\n", hour, min);
    }

    return 0;
}

c program time conversion 24-h to 12-h

1 Answers1