Is my pseudo code for changing time format correct?

Question

I need to create a pseudo code that will prompt for time in 24 hours format, convert it to 12-hour format and also whether it is AM or PM. It will have to repeat until sentinel time of 9999 is entered. Below is what I had come out with, is it correct?

Prompt for time
Get time

Enter this loop:

DOWHILE (time != 9999)

IF (time < 0000 OR time > 2400 OR (time%100 >=60))

Display 'Invalid time'

ELSE

IF (time >= 1200 AND time <= 2400 )

    format  = 'pm'
    hours = (time/100) - 12
    mins = time%100
    Display 'The new time is ', hours, '.', mins, format

ELSE format = 'am'

IF (time/100 = 00 )
    hours = (time/100) + 12
    mins = time%100
    Display 'The time is ', hours, '.', mins, format 

ELSE

    hours = time/100
    mins = time%100
    Display ' 'The time is ', hours, '.', mins, format 

ENDIF

ENDIF

ENDO

Your code is clearly wrong. Given 1300, the answer should be 1.00 PM but your algorithm will print 13.00 PM. Remember that 12.59 PM is 2 minutes before 1.01 PM; this complicates life. — Jonathan Leffler, Mar 21 '14 at 05:02
To check if it's correct, simply work out what the result will be for a few input values. To *get* the correct algorithm, similarly take a few input values with their output values, and determine the steps to go from the one to the other, then generalize it. — Bernhard Barker, Mar 21 '14 at 05:12

score 0 · Answer 1 · answered Mar 21 '14 at 05:16

In Perl:

#!/usr/bin/env perl
use strict;
use warnings;

sub time_12h_to_24h
{
    my($t12) = @_;
    my($hh,$mm,$ampm) = $t12 =~ m/^(\d\d?):(\d\d?)\s*([AP]M?)/i;
    $hh = ($hh % 12) + (($ampm =~ m/AM?/i) ? 0 : 12);
    return sprintf("%.2d:%.2d", $hh, $mm);
}

sub time_24h_to_12h
{
    my($t24) = @_;
    my($hh,$mm) = $t24 =~ m/^(\d\d?):(\d\d?)/;
    my($ampm) = ($hh <12) ? "am" : "pm";
    $hh %= 12;
    $hh += 12 if $hh == 0;
    return sprintf("%d:%.2d %s", $hh, $mm, $ampm);
}

while (<>)
{
    chomp;
    my($input, $entry) = split / - /;
    my $time_24h = time_12h_to_24h($input);
    my $time_12h = time_24h_to_12h($time_24h);
    print "$input - $time_24h : $time_12h - $entry\n";
    #printf "%8s - %5s : %8s - %s\n", $input, $time_24h, $time_12h, $entry;
}

Sample data:

12:00 AM - 0000
12:01 AM - 0001
12:59 AM - 0059
01:00 AM - 0100
11:00 AM - 1100
11:59 AM - 1159
12:00 PM - 1200
12:59 PM - 1259
01:00 PM - 1300
11:59 PM - 2359
12:00 AM - 2400

Sample output:

12:00 AM - 00:00 : 12:00 am - 0000
12:01 AM - 00:01 : 12:01 am - 0001
12:59 AM - 00:59 : 12:59 am - 0059
01:00 AM - 01:00 : 1:00 am - 0100
11:00 AM - 11:00 : 11:00 am - 1100
11:59 AM - 11:59 : 11:59 am - 1159
12:00 PM - 12:00 : 12:00 pm - 1200
12:59 PM - 12:59 : 12:59 pm - 1259
01:00 PM - 13:00 : 1:00 pm - 1300
11:59 PM - 23:59 : 11:59 pm - 2359
12:00 AM - 00:00 : 12:00 am - 2400

Is my pseudo code for changing time format correct?

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