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Range-Based for Loop in C++

C++ do while Loop

Last Updated : 12 Dec, 2024

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In C++, the do-while loop is an exit-controlled loop that repeatedly executes a block of code at least once and continues executing as long as a given condition remains true. Unlike the while loop, the do-while loop guarantees that the loop body will execute at least once, regardless of whether the condition is true or false.

Let’s take a look at an example:

C++

#include <iostream> using namespace std;  int main() {      // do-while loop to print "Hi" 5 times     int i = 0;     do {         cout << "Hi" << endl;         i++;     } while (i < 5);      return 0; }

Output

Hi Hi Hi Hi Hi

Explanation: The above do-while loop prints the text “Hi” 5 times. It first executes the body of the loop and then checks the condition. Since the condition i < 5 is true for the first few iterations, the loop continues running. Once i reaches 5, the condition becomes false, and the loop exits.

Syntax of do-while Loop

do {
// Body of the loop
// Update expression
} while (condition);

We have to define the loop variable beforehand and update it manually in the body of the loop. Notice the semicolon (“;”) in the end of loop. It is compulsory to terminate the do while loop after the semicolon.

The various parts of the do-while loop are:

Condition: The condition is checked after the loop body executes. If the condition evaluates to true, the loop continues. If false, the loop exits.
Update Expression: Update the loop variable bringing it closer to termination condition.
Body: Body: It is a group of statement that will be executed surely for the first time and then till the condition remains true.

Working of do while Loop in C++

Let’s understand the working of the do while loop using the given image:

Control falls into the do-while loop.
The statements inside the body of the loop get executed.
Updation takes place.
The flow jumps to Condition
Condition is tested.
- If the Condition yields true, go to Step 6.
- If the Condition yields false, the flow goes outside the loop
The flow goes back to Step 2.
The do-while loop has been ended and flow has gone outside the loop.

Flow Diagram of do-while loop

do while loop in C++

Examples of do while Loop in C++

The below examples demonstrate the use of do while loop in different cases and situations:

Print Numbers Less than 0

C++

#include <iostream> using namespace std;  int main() {      // do-while loop to print "Hi" 5 times     int i = 1;     do {         cout << i << endl;         i++;     } while (i < 0);      return 0; }

Output

Explanation: As we can see, even though the condition is false from the start, the body is still executed once.

User Input Validation with do-while Loop

Let’s consider an example where a user is prompted to enter a positive number. The program will continue to prompt the user until they enter a valid number.

C++

#include <iostream> using namespace std;  int main() {     int n;      // Do-while loop to ensure user enters a positive number     do {         cout << "Enter a positive number: ";         cin >> n;     } while (n <= 0);      cout << "Entered number: " << n << endl;      return 0; }

Output

Enter a positive number: -1
Enter a positive number: -999
Enter a positive number: 2
Entered number: 2

This is one of the primary applications of do while loop in C++.

Print a Square Pattern using Nested Loops

Just like other loops, we can also nest one do while loop into another do while loop.

C++

#include <iostream> using namespace std;  int main() {     int i = 0;      // Outer loop to print each row     do {         int j = 0;                // Inner loop to print each character         // in each row         do {             cout << "* ";             j++;         } while (j < 4);         cout << endl;         i++;     }while (i < 4);      return 0; }

Output

* * * *  * * * *  * * * *  * * * *

Infinite do while Loop

C++

#include <iostream> using namespace std;  int main() {          // Infinite loop     do {         cout << "gfg" << endl;     }while (true);      return 0; }

Output

gfg
gfg
.
.
.
infinite times

Range-Based for Loop in C++

S

SanghpriyaGautam2

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Article Tags :

C++
CPP-Control-Flow

Practice Tags :

CPP
CPP-Control-Flow

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