Last Updated on December 29, 2023 by Ankit Kochar
Loops are essential constructs for repetitive execution of code, and two commonly used loop structures are the while loop and the do-while loop. While both loops facilitate iteration, they differ in their execution order and conditions. Understanding the distinctions between the while and do-while loops is crucial for choosing the appropriate structure based on the specific requirements of a program.
What is Loop?
A loop’s definition in computer programming is similar to its meaning. Loops are a block of code that executes multiple times. If there were no loops, you would have to write everything you wanted to print repeatedly. A Loop repeats the sequence of statements until the stated condition is false. The loop’s purpose is to repeatedly execute the same code.
What is While Loop?
A while loop is a control flow statement that allows code to be executed multiple times based on a specified Boolean condition. A loop consists of two components: the loop body and the control statement. The control statement is a set of conditions that instructs the loop’s body to continue running until the specified condition is met. The while loop is similar to a looping if statement.
We check the condition at the beginning of the loop structure in this loop. A code block will run until the condition is true, at which point the loop will be terminated or ended. We call it an infinite loop if the condition remains true.
A While loop is the most basic looping structure. It is a loop with an entry control. A while loop evaluates a condition before processing the loop’s body. If a condition is true, the body of a loop is executed, and only then.
After the body of a loop is completed, the control returns to the beginning, and the condition is checked. If it is true, the same procedure is followed until the condition is false. When the condition is false, the control exits the loop.
If the condition in a while loop is not true, the body of the loop will not be executed, not even once.
Syntax of While Loop
while (boolean condition)
{
loop statements...
}Flowchart of While Loop
Example of While Loop
Below we have code implementation and explanation of While loop.
#include <iostream>
using namespace std;
int main() {
int count = 1;
while(count<=5)
{
cout<<count<<" ";
count+=1;
}
return 0;
} Output
1 2 3 4 5Explanation
This while loop repeatedly executes the block of code inside it as long as the condition count <= 5 is true. The variable count starts at 1, and each time the loop executes, it prints the current value of the count and increments it by 1. This continues until the count reaches 6, at which point the loop terminates.
Do-While Loop
A Do-while loop is similar to a while loop with the exception that the condition is always executed after the loop body. It's also known as an exit-controlled loop.
The body of a loop is always executed at least once in the do-while loop. It checks the condition after the body has been executed. If the condition is met, the body of the loop will be executed once more. Otherwise, control is removed from the loop.
Syntax of Do-While Loop
do
{
statements..
}
while (condition);Flowchart of Do-While Loop
Example of the Do-While Loop
Below we have code implementation and explanation of do While loop
#include <iostream>
using namespace std;
int main() {
int i = 1;
do {
cout << i << endl;
i++;
} while (i <= 5);
return 0;
}
Output
1
2
3
4
5Explanation
In the above c++ program , this do-while loop count from 1 to 5, printing each number as it goes. The loop is executed at least once, regardless of the condition. Once i reaches 6, the loop terminates, and the program proceeds to the next step.
Difference between While and Do-While Loop
Here we have the difference between while and do while loop
| While | Do While |
|---|---|
| In while loop condition is checked first and then the statement is executed | In do-while statement is executed at least once thereafter condition is checked |
| It follows top-down approach | It follows bottom-up approach |
| For single statement, we do need to add brackets | In do white brackets are always needed |
| While loop is entry controlled loop | Do while is an exit controlled loop |
| Here “while” keyword is used | Here “do while” keyword is used |
| If the condition is false initially, the loop body is never executed | The loop body is executed at least once, regardless of the initial condition |
Conclusion
The while and do-while loops in C provide programmers with powerful tools for executing repetitive tasks. While both loops share the common goal of iteration, their differences in initialization and termination conditions impact their application. The while loop is suitable for scenarios where the condition is checked before the first iteration, while the do-while loop ensures that the loop body is executed at least once before checking the condition. The choice between the two depends on the specific logic and requirements of the program.
Frequently Asked Questions related to Difference Between While and Do While Loop
Here are the FAQ related to Difference Between While and Do While Loop:
1. What is the main difference between the while and do-while loops?
The key difference lies in when the loop condition is checked. In the while loop, the condition is checked before the first iteration, potentially resulting in zero iterations. In the do-while loop, the condition is checked after the first iteration, ensuring that the loop body is executed at least once.
2. When should I use a while loop?
Use the while loop when you want to check the loop condition before entering the loop body. This loop structure is suitable when the loop may not need to execute at all if the condition is initially false.
3. When should I use a do-while loop?
Use the do-while loop when you want to ensure that the loop body is executed at least once, regardless of the initial condition. This loop is useful when you need to perform an action before checking the loop condition.
4. Can the loop condition be omitted in a do-while loop?
No, the loop condition in a do-while loop cannot be omitted. The loop body is always executed at least once before checking the condition. However, in a while loop, the condition can result in zero iterations if initially false.
5. Which loop is more appropriate for validating user input?
The do-while loop is often preferred for validating user input because it ensures that the input validation code is executed at least once. This can prompt the user for input until valid data is provided, making it suitable for interactive scenarios.