LOOP in C++

Looping is used in the C++ when the repetition of a block of statements is required. Loop permits you to repeatedly execute a block of statements.

Suppose we want to print “codingtag” 11 times, this can be possible by the iterative method i.e. in the code, you need to write the cout() statement 11 times. For example


 


// C++ program to illustrate need of loops

#include <iostream>
using namespace std;
int main()

{
          cout << "codingtag\n";
          cout << "codingtag\n";
          cout << "codingtag\n";
          cout << "codingtag\n";
          cout << "codingtag\n";
          cout << "codingtag\n";
          cout << "codingtag\n";
          cout << "codingtag\n";
          cout << "codingtag\n";
          cout << "codingtag\n";
          cout << "codingtag\n";
          return 0;
}

Result:

codingtag

codingtag

codingtag

codingtag

codingtag

codingtag

codingtag

codingtag

codingtag

codingtag

codingtag

…….

This method is long and will become complex if the no of time increases. This problem can be easily solved by looping because the statement required to be written only once and the loop will be executed 11 times. It will be illustrated in further examples.

In other words, the loop can be defined as the sequence of the various instructions which will repeat until the specific condition is reached.

There are two types of loop are available in C++ programming language:

  • Entry Control loop
  • Exit Control loop

Entry Control loop

Firstly, the condition is tested before entering the body of the loop.

Example:

  1. For
  2. While loop

Exit Control loop

The test condition is evaluated at the end of the loop body which means the body of the loop will execute at least once regardless of the test conditions, whether it is true or false.

Example

do – while loop

For loop

For loop is known as the entry controlled loop or repetition control structure which permits the user to write a loop that executes a specific line to a number of times. The user can be able to perform n number of steps with a single statement.

The syntax used for the “For loop” declaration is as under:

For (initialization expression; test expression; update expression)

{

// loop body

// statements required to be executed

}

Where,

Initialization expression is to initialize the loop counter to any value that may be int k = 9;

Test expression is used for evaluating the condition

Update expression is used to increments/decrements the loop variable by a certain value i.e. it can be k++ or k–

Working of “For Loop”

Firstly, the initialization statement executes at the beginning after that the test expression is verified. If the test expression is wrong, for loop is terminated but if the test expression is not wrong, the inside code in the body will execute and update expression is updated. After that, the test expression is evaluated again and this process will continue until the test expression is false.

 

// A program to illustrate the For loop in C++

#include <iostream>
using namespace std;
int main()
{
          for (int i = 1; i <= 11; i++)
          {
                     cout << "Codingtag\n";
          }
          return 0;
}

Result:

Codingtag

Codingtag

Codingtag

Codingtag

Codingtag

Codingtag

Codingtag

Codingtag

Codingtag

Codingtag

Codingtag


WHILE LOOP

In while loop, firstly the condition is evaluated and if the condition is true it will execute inside statements and it will be repeated continuously until the condition returns false. Once the condition return false, the control comes out and jump to the further statement after while loop.

Syntax

while(condition)
{
Statement;
}

Where the statement can be single or block and condition can be any expression. When the condition is true, the loop iterates meanwhile, the condition is true. Program control passes the line instantly following the loop when the condition becomes false.

Program to illustrate while loop in C++

#include <iostream>
using namespace std;
int main ()
{
   // declaration Local variable:
   int j = 14;
   // execution of while loop
   while( j < 25 ) {
   cout << "value of j: " << j << endl;
   j++;
}
  return 0;
}

Result:

value of j: 14

value of j: 15

value of j: 16

value of j: 17

value of j: 18

value of j: 19

value of j: 20

value of j: 21

value of j: 22

value of j: 23

value of j: 24


DO WHILE LOOP

Do while loop is very similar to while loop. Since a while loop can be used to repeat a block of statements until the condition of the given loop returns false. The prime difference between do-while and while loop is the condition is first evaluated after that statement gets executed in while loop whereas in a do-while loop, the inside statements executed firstly and then the evaluation of condition take place.

Syntax

do
{
Statement(s);
}
while(condition);

Example of Do while Loop

#include <iostream>
using namespace std;
int main(){
   int a = 1;
   do{
      cout<<"The number value is "<<a<<endl;
      a++;
   } while(a <= 6);
   return 0;
}

Result:

The number value is 1

The number value is 2

The number value is 3

The number value is 4

The number value is 5

The number value is 6


NESTED LOOP

When a loop is placed inside the body of another loop is known as nested loop.

while(condition first)
{
Statement(s);
While(condition second)
{
Statement(s);
… … …
}
… … …
}

There is various nested loop present in i.e. nested for loop, nested do while loop and nested while loop. A number of loops is based upon the number of complexity of the program.

Following are the example of for nested loop

#include <iostream>
using namespace std;
int main () {
   int i, j;
     for(i = 6; i<50; i++) {
     for(j = 6; j <= (i/j); j++)
         if(!(i%j)) break; // if factor found, not prime
         if(j > (i/j)) cout << i << " is prime\n";
   }
   return 0;
}

Result:

6 is prime

7 is prime

8 is prime

9 is prime

10 is prime

11 is prime

12 is prime

13 is prime

14 is prime

15 is prime

16 is prime

17 is prime

18 is prime

19 is prime

20 is prime

21 is prime

22 is prime

23 is prime

24 is prime

25 is prime

26 is prime

27 is prime

28 is prime

29 is prime

30 is prime

31 is prime

32 is prime

33 is prime

34 is prime

35 is prime

37 is prime

38 is prime

39 is prime

40 is prime

41 is prime

43 is prime

44 is prime

45 is prime

46 is prime

47 is prime

Leave a Reply

avatar
  Subscribe  
Notify of