🟡 Control Flow · Lesson 18

while and do-while Loops

What is while and do-while Loops?

while and do-while Loops
while loop checks condition before execution. do-while loop executes at least once and then checks condition.

Level
🟡 Control Flow and Core Programming

Example File
while-do-while.cpp

Main Focus
Concept + syntax + practical C++ program

Why should you learn this?

It helps you write correct and readable C++ programs.
It is used repeatedly in school practicals, projects and competitive programming.
It builds the base for advanced topics such as OOP, STL and data structures.

Important Terms

Term	Meaning / Use
while	While used in while and do-while Loops programming.
do while	Do while used in while and do-while Loops programming.
condition	Condition used in while and do-while Loops programming.
entry-controlled	Entry-controlled used in while and do-while Loops programming.
exit-controlled	Exit-controlled used in while and do-while Loops programming.

Syntax / Pattern

while(condition){ } and do { } while(condition);

Example Program

#include <iostream>
using namespace std;
int main(){
    int n = 3;
    while(n > 0){
        cout << n << " ";
        n--;
    }
    return 0;
}

Expected Output

3 2 1

Program Explanation

while checks n > 0 before every iteration.
n-- moves the loop towards termination.

Exam Tip: In C++ practical answers, write the logic first, then the program, then expected output. For theory, always include one suitable example.

Where will you use it?

input validation
menu repetition
unknown repetitions

Common Mistakes

Not updating loop variable.
Forgetting semicolon after do-while.

Practice Tasks

Create a password retry loop.
Print digits of a number.

Summary

while and do-while Loops is an important C++ topic. Learn the definition, understand the syntax, run the example program and then solve the practice tasks to make the concept strong.