C Program to Convert time from 24 hour to 12 hour format

In this tutorial, we will learn how to write a C program to convert 24 hour time format to 12 hour time format.

For example:

Input: 23 59
Output: 11:59 PM

C Program for 24 hour time to 12 hour time conversion

Let’s write a program for this conversion. The detailed explanation of the program is at the end of this article.

#include <stdio.h>
#include <string.h>

// Function to convert time from 24-hour to 12-hour format
void convert24To12(int hour, int minute) {
    int hour12;     // Variable to hold the converted hour
    char period[3]; // Array to hold "AM" or "PM"

    // Find the appropriate 12-hour format and period (AM/PM)
    if (hour == 0) {
        hour12 = 12;
        strcpy(period, "AM");
    } else if (hour < 12) {
        hour12 = hour;
        strcpy(period, "AM");
    } else if (hour == 12) {
        hour12 = 12;
        strcpy(period, "PM");
    } else {
        hour12 = hour - 12;
        strcpy(period, "PM");
    }

    // Print the time in 12-hour format
    printf("%02d:%02d %s\n", hour12, minute, period);
}

int main() {
    // Variables to hold user input
    int hour, minute; 

    // Prompt user to enter time in 24-hour format
    printf("Enter time in 24-hour format (HH MM): ");
    scanf("%d %d", &hour, &minute); // Read user input

    // Checks if the user entered time is in valid range
    if (hour < 0 || hour >= 24 || minute < 0 || minute >= 60) {
        // Print error message if user input is found invalid
        printf("Invalid data!\n"); 
    } else {
        // If entered time is valid then call convert24To12() for conversion
        convert24To12(hour, minute); 
    }
    return 0;
}

Output 1:

Enter time in 24-hour format (HH MM): 00 45
12:45 AM

Output 2:

Enter time in 24-hour format (HH MM): 12 00
12:00 PM

Output 3:

Enter time in 24-hour format (HH MM): 25 10
Invalid data!

Explanation of the program:

Header Files:

• #include <stdio.h>: It is included so that we can use input/output functions such as printf and scanf.
• #include <string.h>: It is included so that we can use strcpy function for copying strings.

Function Definition:

void convert24To12(int hour, int minute) {
    int hour12;
    char period[3];

• convert24To12: This function takes two integer arguments hour and minute, These arguments are in 24-hour format.
• hour12: This variable will store hour in 12-hour format after conversion.
• period: This array will store the “AM” or “PM” string.

Conversion Logic:

    if (hour == 0) {
        hour12 = 12;
        strcpy(period, "AM");
    } else if (hour < 12) {
        hour12 = hour;
        strcpy(period, "AM");
    } else if (hour == 12) {
        hour12 = 12;
        strcpy(period, "PM");
    } else {
        hour12 = hour - 12;
        strcpy(period, "PM");
    }

• If hour is 0, then hour12 is 12 and period is AM.
• If hour is less than 12, then hour12 is equal to hour and period is AM.
• If hour is 12, then hour12 is 12 and period is PM.
• If hour is greater than 12, then hour12 is (hour – 12) and period is PM.

Input Validation:

    if (hour < 0 || hour >= 24 || minute < 0 || minute >= 60) {
        printf("Invalid data!\n");
    } else {
        convert24To12(hour, minute);
    }

    return 0;
}

• The program checks if the entered hour is between 0 and 23 and minute is between 0 and 59. If not, it prints an error message “Invalid data!”.
• If the input is valid, then it calls convert24To12 function for conversion.

Related C Programs:

• C Program to convert time from 12 hour format to 24 hour format
• C Program to print the day for input date, month and year
• C Program to print current date and time
• Java – Convert string to 24 hour time format
• Java – Convert 12 hour format to 24 hour format and vice versa