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Program to convert time from 12 hour to 24 hour format

  • Difficulty Level : Easy
  • Last Updated : 16 Aug, 2021

Given a time in 12-hour AM/PM format, convert it to military (24-hour) time. 
Note: Midnight is 12:00:00 AM on a 12-hour clock and 00:00:00 on a 24-hour clock. Noon is 12:00:00 PM on 12-hour clock and 12:00:00 on 24-hour clock

Examples:

Input : A single string containing a time in 12-hour 
clock format(hh:mm:ss AM or hh:mm:ss PM
        where 01 <= hh <= 12 or 01 <= mm,ss <= 59 
Output :Convert and print the given time in 24-hour format,
where 00 <= hh <= 23

Input : 07:05:45PM
Output : 19:05:45

C++




// C++ program to convert 12 hour to 24 hour
// format
#include<iostream>
using namespace std;
 
void print24(string str)
{
    // Get hours
    int h1 = (int)str[1] - '0';
    int h2 = (int)str[0] - '0';
    int hh = (h2 * 10 + h1 % 10);
 
    // If time is in "AM"
    if (str[8] == 'A')
    {
        if (hh == 12)
        {
            cout << "00";
            for (int i=2; i <= 7; i++)
                cout << str[i];
        }
        else
        {
            for (int i=0; i <= 7; i++)
                cout << str[i];
        }
    }
 
    // If time is in "PM"
    else
    {
        if (hh == 12)
        {
            cout << "12";
            for (int i=2; i <= 7; i++)
                cout << str[i];
        }
        else
        {
            hh = hh + 12;
            cout << hh;
            for (int i=2; i <= 7; i++)
                cout << str[i];
        }
    }
}
 
// Driver code
int main()
{
   string str = "07:05:45PM";
   print24(str);
   return 0;
}

Java




// Java program to convert 12 hour
// format to  24 hour format
class GFG
{
static void print24(String str)
{
    // Get hours
    int h1 = (int)str.charAt(1) - '0';
    int h2 = (int)str.charAt(0) - '0';
    int hh = (h2 * 10 + h1 % 10);
 
    // If time is in "AM"
    if (str.charAt(8) == 'A')
    {
        if (hh == 12)
        {
            System.out.print("00");
            for (int i = 2; i <= 7; i++)
                System.out.print(str.charAt(i));
        }
        else
        {
            for (int i = 0; i <= 7; i++)
                System.out.print(str.charAt(i));
        }
    }
 
    // If time is in "PM"
    else
    {
        if (hh == 12)
        {
            System.out.print("12");
            for (int i = 2; i <= 7; i++)
                System.out.print(str.charAt(i));
        }
        else
        {
            hh = hh + 12;
            System.out.print(hh);
            for (int i = 2; i <= 7; i++)
                System.out.print(str.charAt(i));
        }
    }
}
 
// Driver code
public static void main (String[] args)
{
    String str = "07:05:45PM";
    print24(str);
}
}
 
// This code is contributed by Anant Agarwal.

Python3




# Python3 program to convert 12
# hour to 24 hour format
def print24(s):
 
    # Get hours
    h1 = ord(s[1]) - ord('0')
    h2 = ord(s[0]) - ord('0')
    hh = (h2 * 10 + h1 % 10)
  
    # If time is in "AM"
    if (s[8] == 'A'):
        if (hh == 12):
            print('00', end = '')
             
            for i in range(2, 8):
                print(s[i], end = '')
 
        else:
            for i in range(0, 8):
                print(s[i], end = '')
  
    # If time is in "PM"
    else:
        if (hh == 12):
            print("12", end = '')
             
            for i in range(2, 8):
                print(s[i], end = '')
         
        else:
            hh = hh + 12;
            print(hh, end = '')
             
            for i in range(2, 8):
                print(s[i], end = '')
             
# Driver code          
if __name__=="__main__":
 
   s = "07:05:45PM"
    
   print24(s)
    
# This code is contributed by rutvik_56

C#




// C# program to convert 12 hour
// format to 24 hour format
using System;
 
class GFG
{
     
static void print24(String str)
{
    // Get hours
    int h1 = (int)str[1] - '0';
    int h2 = (int)str[0] - '0';
    int hh = (h2 * 10 + h1 % 10);
 
    // If time is in "AM"
    if (str[8] == 'A')
    {
        if (hh == 12)
        {
            Console.Write("00");
            for (int i = 2; i <= 7; i++)
                Console.Write(str[i]);
        }
        else
        {
            for (int i = 0; i <= 7; i++)
                Console.Write(str[i]);
        }
    }
 
    // If time is in "PM"
    else
    {
        if (hh == 12)
        {
            Console.Write("12");
            for (int i = 2; i <= 7; i++)
                Console.Write(str[i]);
        }
        else
        {
            hh = hh + 12;
            Console.Write(hh);
            for (int i = 2; i <= 7; i++)
                Console.Write(str[i]);
        }
    }
}
 
// Driver code
public static void Main(String[] args)
{
    String str = "07:05:45PM";
    print24(str);
}
}
 
// This code is contributed by Rajput-Ji

Javascript




<script>
// javascript program to convert 12 hour
// format to 24 hour format
  
 
  function print24(str)
{
    // Get hours
    var h1 = Number(str[1] - '0');
    var h2 = Number(str[0] - '0');
    var hh = (h2 * 10 + h1 % 10);
  
    // If time is in "AM"
    if (str[8] == 'A')
    {
        if (hh == 12)
        {
            document.write("00");
            for (var i = 2; i <= 7; i++)
                document.write(str[i]);
        }
        else
        {
            for (var i = 0; i <= 7; i++)
                document.write(str[i]);
        }
    }
  
    // If time is in "PM"
    else
    {
        if (hh == 12)
        {
            document.write("12");
            for (var i = 2; i <= 7; i++)
                document.write(str[i]);
        }
        else
        {
            hh = hh + 12;
            document.write(hh);
            for (var i = 2; i <= 7; i++)
                document.write(str[i]);
        }
    }
}
  
// Driver code
 
    var str = "07:05:45PM";
    print24(str);
 
// This code is contributed by bunnyram19.
</script>

Output: 

19:05:45

Method 2: Using java Date

Java




// Java program for the above approach
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
 
class GFG {
    public static String englishTime(String input)
        throws ParseException
    {
 
        // Format of the date defined in the input String
        DateFormat dateFormat
            = new SimpleDateFormat("hh:mm:ss aa");
       
        // Change the pattern into 24 hour format
        DateFormat formate
            = new SimpleDateFormat("HH:mm:ss");
        Date time = null;
        String output = "";
       
        // Converting the input String to Date
        time = dateFormat.parse(input);
       
        // Changing the format of date
        // and storing it in
        // String
        output = formate.format(time);
        return output;
    }
 
    // Driver Code
    public static void main(String[] arg)
        throws ParseException
    {
        System.out.println(englishTime("07:05:45 PM"));
    }
}

Output:

19:05:45

This article is contributed by Rahul singh (Nit kkr). If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
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