Loop Statements in C++

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22 Aug 2022

Intermediate

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In general, C++ programming language follows a sequential execution approach. The first statement is executed and then the compiler moves to the next statement in line. In case of a conditional statement, the statement is executed depending on the result of the condition. In addition, you can use looping statements in C++ when you want to repeat the execution of a specific block of code till a specific condition is satisfied. For example, you want to print numbers from 1 to 10. Instead of manually writing the code with 10 separate print statements, you can define a loop statement and let the compiler to manually increment the value after every iteration and print the value. You can finish writing this piece of code in just 2-3 lines.

The looping statements available in C++ are :

For loop
While loop
Do .. While loop

For Loop

For loop can be used in C++ programming to repeat a specific execution for specific number of times. This helps us to avoid writing multiple lines of code and bring everything into a single line. The syntax of for loop is :

 for (variable initialization; condition; increment operation)
 {
 //loop statements;
 }

The initialization step allows you to declare and initialize a variable. In the next step, you can evaluate the variable against a condition and in the final step, you can increment or decrement the value of the variable. The loop will execute till the condition becomes false. Then, the program will exit the loop and continue with the rest of the statements.

Example Program

 #include <iostream>
 using namespace std;
 
 int main()
 {
 int a;
 for (a=1; a<=10; a++)
 {
 cout << "The value of a is: " << a << '\n';
 }
 }

The output of this program will be :

While Loop

While loop can be used when you want to a statement to execute continuously till the condition specified is true. The difference between for loop and while loop is with for loop, you will know how many times the loop will execute. With while loop, you will not know the number of iterations till the program exits from the loop when the condition does not match. The syntax of for loop is :

 while (condition)
 {
 //loop statements;
 }

Example Program

 #include <iostream>
 using namespace std;
 
 int main()
 {
 int a=1;
 while (a<=10)
 {
 cout << "The value of a is: " << a << '\n';
 a++; 
 }
 }

The output of this program will be :

Do .. While Loop

The basic difference between for loop, while loop and do while loop is that in do while loop, the condition is checked at the bottom of the loop. In the do while loop, the body of the loop will be executed first and then the condition will be evaluated. This ensures that the statement is executed at least once even if the condition is not satisfied. The syntax of do while loop is :

 do
 {
 // statement execution;
 }
 while(condition);

Example Program

 #include <iostream>
 using namespace std;
 
 int main()
 {
 string a;
 do
 {
 cout <<"Enter a word: " << '\n';
 cin >> a;
 cout << "You entered the word: " << a << '\n';
 }
 while (a != "bye"); 
 }