Question

I am writing a C program to take in a value representing a time of the day in 24 hour format, and a time duration in similar format, positive or negative. This program should calculate the 24 hour time after the duration (that is, beginning + duration = end). For example, 1345 and 345 would output 1730.

However, I have no idea how to handle improper inputs. For example, values like 2372 or 2520 shouldn’t be accepted. As well, if I have (for example) 100 and -200, I should get 2300 as output instead of -100. In short, I know that the first two numbers should be mod 24, and the last two numbers should be mod 60, but I don’t know how to apply these operations to the input. Can anyone offer any tips on how I can do this?

Answer 1

Read the input as an int, separate the minutes from the hours and check both of them:

int tm, h, m, is_negative = 0;
scanf("%d", &tm);

if (tm < 0) {
    is_negative = 1;
    tm = -tm;
}

m = tm % 100; // separates the two last digits
h = tm / 100; // excludes the two last digits

if (m > 59) {
    handle_error();
}

if (h > 23) {
    handle_error();
}