Programming C in Loop While do

Understanding the Do-While Loop in C Programming

Hey there, coding adventurer!
Today, we’re going to learn about another type of loop called the Do-While Loop. The cool thing about this loop is that it guarantees the code inside the loop will run at least once, even if the condition is false. Let’s dive in and see how it works!

What is a Do-While Loop?

A Do-While Loop is similar to a While Loop, but the main difference is that the condition is checked after the loop runs, not before. This means that the code inside the loop will always run at least one time, no matter what.

Syntax of Do-While Loop

Here’s how you write a Do-While Loop in C:

do {
    // Code to be repeated
} while (condition);

Code: This is the block of code that will run first.
Condition: After the code runs once, the loop checks if the condition is true. If it’s true, the loop runs again. If it’s false, the loop stops.

Real-Life Example of a Do-While Loop

Imagine you’re trying to guess a number, and the computer keeps asking for your guess. Even if your first guess is correct, the computer has to ask for at least one guess. This is exactly how the Do-While Loop works—it asks you for a guess at least once, and then it keeps going if your guess is wrong.

Here’s a simple program that prints the numbers from 1 to 5 using a Do-While Loop:

#include <stdio.h>

int main() {
    int i = 1;  // Initialization

    do {
        printf("%d\n", i);  // Print the current value of i
        i++;  // Increment the counter
    } while (i <= 5);  // Condition to check

    return 0;
}

Explanation:

Initialization: We start with i = 1.
The code inside the loop prints the value of i.
After printing, i is incremented by 1.
The loop keeps running until i becomes greater than 5.

Output:

Flowchart of a Do-While Loop

Here’s how the Do-While Loop works step by step:

Run the code inside the loop.
Check the condition.
If the condition is true, go back and run the code again.
If the condition is false, stop the loop.

    [Start]
       |
  [Run code once]
       |
  [Check condition]
    /      \
  Yes      No
  |         |
[Run code] [End]
  |
[Repeat loop]

Programming Example: Password Check

Let’s write a program that asks for a password and keeps asking until the correct password is entered, but it will ask for the password at least once.

#include <stdio.h>

int main() {
    int password;

    do {
        printf("Enter the password: ");
        scanf("%d", &password);
    } while (password != 1234);  // Keep asking until the correct password is entered

    printf("Access granted!\n");

    return 0;
}

Explanation:

The program will ask for the password at least once, even if the correct password is entered on the first try.
If the password is incorrect, it will keep asking for the password until password == 1234.

Output:

Enter the password: 1111
Enter the password: 4321
Enter the password: 1234
Access granted!

Difference Between While and Do-While Loop

While Loop: The condition is checked before the loop runs. If the condition is false, the loop might not run at all.
Do-While Loop: The code runs at least once, and the condition is checked after the first run.

For example, let’s say we have a condition that is false from the start. Here’s how a While Loop would behave:

int i = 6;
while (i <= 5) {
    printf("%d\n", i);  // This will not run because the condition is false
}

Output:

Nothing is printed because i is not less than or equal to 5.

Now, look at the same condition with a Do-While Loop:

int i = 6;
do {
    printf("%d\n", i);  // This will run at least once
} while (i <= 5);

Output:

The loop runs once, even though the condition is false from the beginning.

Real-Life Fun Example: Asking for a Name

Let’s write a program where the computer asks for your name and says hello, even if you don’t input anything. It will keep asking for a name until you enter a valid one.

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

int main() {
    char name[20];

    do {
        printf("What's your name? ");
        scanf("%s", name);
    } while (strlen(name) == 0);  // Keep asking if the name is empty

    printf("Hello, %s!\n", name);

    return 0;
}

Explanation:

The program asks for your name at least once.
It will keep asking if no name is provided (an empty string).

Output:

What's your name? 
What's your name? John
Hello, John!

Challenge Time!

Here’s a challenge for you: Write a program that prints the multiplication table for the number 5, using a Do-While Loop.

Here’s the solution:

#include <stdio.h>

int main() {
    int i = 1;
    int num = 5;

    do {
        printf("%d x %d = %d\n", num, i, num * i);
        i++;  // Increment i
    } while (i <= 10);  // Continue until i is greater than 10

    return 0;
}

Output:

5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
...
5 x 10 = 50

Summary

The Do-While Loop ensures that the code inside the loop runs at least once, no matter what.
After the first run, it checks the condition to decide if it should run again.
It’s useful when you need to make sure something happens at least once before checking a condition.

With the Do-While Loop, you can write programs that guarantee at least one execution of a block of code before checking conditions. Keep practicing, and soon you’ll be looping like a pro!