Convert 12 hours to 24 hours in PHP - php

Question

This is my homework in which I was asked to convert time from 12 hours to 24 hours where time was provided in this format 05:09:15AM. I am new to programming, that's why instead of going into loops I decided to do it with conditional statements. So, I created 4 conditions (I used conditions as shown here)
What's the problem then? The problem is I am getting an error stating $_time variable is undefined when I am printing $_time. As per my understanding, this is happening because the $_time variable is inside the functions. But, if that's the case, can you guide me how to do this?
<?php
$_a = ("07:29:23PM");
$_a = explode(':',$_a);
if($_a[0] == 12 && $_a[1] <= 59 && strpos("PM", $_a[2] !== FALSE))
{
$_rpl = str_replace("PM","",$_a[2]);
$_time = $_a[0].":".$_a[1].":".$_rpl;
}
elseif($_a[0] < 12 && $_a[1] <= 59 && strpos("PM", $_a[2] !== FALSE))
{
$_a[0] += 12;
$_rpl = str_replace("PM","",$_a[2]);
$_time = $_a[0].":".$_a[1].":".$_rpl;
}
elseif($_a[0] == 12 && $_a[1] <= 59 && strpos("AM", $_a[2] !== FALSE))
{
$_a[0] = 00;
$_rpl = str_replace("AM","",$_a[2]);
$_time = $_a[0].":".$_a[1].":".$_rpl;
}
elseif($_a[0] < 12 && $_a[1] <= 59 && strpos("AM", $_a[2] !== FALSE))
{
$_rpl = str_replace("AM","",$_a[2]);
$_time = $_a[0].":".$_a[1].":".$_rpl;
}
echo $_time;
?>

Answer 1

In your code there are few errors. The strpos syntax is wrong.
strpos("PM", $_a[2] !== FALSE) // this is incorrect
This you have to write
strpos($_a[2],"PM") //string first and search second.
This will return a integer, position of search string in the string, so don't use false instead use >-1
strpos($_a[2],"PM") > -1) //this is the correct method.
Also define $_time; in the starting and initialise it.
<?php
$_a = ("07:29:23PM");
$_a = explode(':',$_a);
$_time = ""; //initialised the variable.
if($_a[0] == 12 && $_a[1] <= 59 && strpos($_a[2],"PM") > -1)
{
$_rpl = str_replace("PM","",$_a[2]);
$_time = $_a[0].":".$_a[1].":".$_rpl;
}
elseif($_a[0] < 12 && $_a[1] <= 59 && strpos($_a[2],"PM")>-1)
{
$_a[0] += 12;
$_rpl = str_replace("PM","",$_a[2]);
$_time = $_a[0].":".$_a[1].":".$_rpl;
}
elseif($_a[0] == 12 && $_a[1] <= 59 && strpos($_a[2],"AM" ) >-1)
{
$_a[0] = 00;
$_rpl = str_replace("AM","",$_a[2]);
$_time = $_a[0].":".$_a[1].":".$_rpl;
}
elseif($_a[0] < 12 && $_a[1] <= 59 && strpos( $_a[2],"AM")>-1)
{
$_rpl = str_replace("AM","",$_a[2]);
$_time = $_a[0].":".$_a[1].":".$_rpl;
}
echo $_time;
?>
Actually, initialising variable was not causing the error. Error was in your strpos syntax, so none of the if condition was true, so no code executed, so while trying to echo $_time; it was undefined. But its good practice to initialise a variable in the starting itself.

Answer 2

You have inbuilt functions to convert the datetime objects. You can refer php manual for that.
If you want to convert manually, you can do like this.
<?php
$_a = ("10:29:23PM");
$_a = explode(':',$_a);
if(strpos( $_a[2],"PM") > -1) //if PM given
{
$_a[2] = str_replace("PM","",$_a[2]); //remove the PM
if($_a[0] <12) //if time less than 12
$_a[0] = $_a[0] + 12; //then add 12 hours
}
if(strpos( $_a[2],"AM") > -1) //if AM given
{
$_a[2] = str_replace("AM","",$_a[2]); //remove AM
if($_a[0]=='12') //if 12 AM
$_a[0]='00'; //make it 0
}
$newtime = $_a[0].':'.$_a[1].':'.$_a[1];
echo $newtime;
?>

Answer 3

The main point is only changing on hour value, adding +12 if PM and change to 00 if AM.
<?php
$s = "07:05:45PM";
$s = explode(':',$s);
$time = substr($s[2],2,4);
$s[2] = substr($s[2],0,2);
if($time == "PM") {
if($s[0] != "12")
$s[0] = $s[0]+12;
}
if($time == "AM") {
if($s[0] == "12")
$s[0] = "00";
}
echo implode(":",$s);
?>

Answer 4

$string="10:29:23PM";
$a=substr($string, 0, 8);
$b= substr($string, 8, 10);
$dates=$a." ".$b;
// 12-hour time to 24-hour time
echo $time_in_24_hour_format = date("H:i:s", strtotime("$dates"));
// 22:29:23
echo $time_in_24_hour_format = date("H:i", strtotime("$dates"));
// 22:29