while loop in C++ with examples

The execution of while-loop is similar to for-loop in C++. but wherein the while-loop up-dation is a part of the body of loop while in the for-loop is not.

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 In both loops, the execution sequence is in the same order. means, the first is the variable initialization, then the condition is given if the condition is true then the body of  loop is executed then the initialization value is updated or increased. thus a while-loop is executed. but as soon as the condition is false the loop gets terminated.

syntax

initialization;
 while(condition)
   {
     body of loop;
     updation;
   }

while-loop flow diagram in C++

a while-loop flow-diagram as follows,

Here is the program,

Example of while loop in C++

#include<iostream>
using namespace std;

 int main()
 {
   
   int num=5;

   int i=0; 
   while(i<num) 
    {
      cout<<i+1<<"statement executed\n"; // body of loop
      i++;
    }

 return 0;
 }

OUTPUT

1.statement executed
2.statement executed
3.statement executed
4.statement executed
5.statement executed

Explanation

In the Program, we declared loop size  by num = 5, so here loop is executed 5 times,

After initialization variable i to 0, then after the condition is checked which is becoming true (0<5) so body of loop is executed.

In the last, variable i value is increased by 1, Thus a while-loop will be executed.

Now the whole procedure begins again until the condition becomes  false (5<5) meaning that the condition will be checked again because this times variable value increased by 1 so the condition will be (1<5)
and we know this time condition also becoming true so body of loop is executed again.

Here is another way,

above program, implementation is given in the below table

initialization value (i=1)	condition check (i<=5)	body of loop executed
0	0<5	1.statement executed
1	1<5	2.statement executed
2	2<5	3.statement executed
3	3<5	4.statement executed
4	4<5	5.statement executed
5	5<5	Exit

the execution sequence of while loop will as,

in the while-loop loop following are will repeat, until the condition becomes false,

nested while-loop in C++

when a while-loop is body of another while-loop is called nested while loop in C++.

syntax

while (expression) 
  {
  // outer-while body
    while(expression)
      {
        // inner-while body
        updation;
      } 
      updation;
  |

Let’s try with an example,

Example of nested while loop in C++

In the program outer while execute 3 times while inner while-loop execute 2 times,

#include<iostream.h>
using namespace std; 
 
 int main()
 {
   
   int i=1,j; 
   while(i<=3) 
    {
//outer-while body
      cout<<i<<"outer-while loop\n"; 
      j=1;
      while(j<=2) 
        {
          cout<<"\t"<<j<<"inner-while loop\n";
          j++;
        }
      i++;
   }
return 0;
 }

OUTPUT

1.outer-while loop
    1.inner-while loop 
    2.inner-while loop
2.outer-while loop
    1.inner-while loop
    2.inner-while loop 
3.outer-while loop
    1.inner-while loop 
    2.inner-while loop

Explanation

repetition of nested while-loop will as follows,

while-loop with for-loop Example in C++

syntax

while (expression) 
  { 
   // outer-while body 
    for(..........) 
      {
         // inner-while body updation; 
      } 
     updation; 
  |

while-loop with for-loop will execute same as the nested while-loop,

#include<iostream>
using namespace std; 
 
 int main()
 {
  
   int i=1,j;
   while(i<=3) 
    {
//outer-while body
      cout<<i<<".while-loop executed\n";

      for(j=1; j<=2; j++)
	  cout<<"\t"<<j<<".for-loop executed\n";
      
      i++;
   }
return 0;
 }

OUTPUT

1.while-loop executed
    1.for-loop executed
    2.for-loop executed
2.while-loop executed     
    1.for-loop executed
    2.for-loop executed
3.while-loop executed    
    1.for-loop executed
    2.for-loop executed

Let’s try another example

#include<iostream>
using namespace std; 
 
int main()
 {
   int num;
  
   cout<<"Enter number: ";
   cin>>num;

   int row=1,col;
   while(row<=10)
    {

//while-loop body
      for(col=1; col<=num; col++)
	 cout<<row<<"x"<<col<<"="<<row*col<<"\t";// for-loop body

      row++;
      cout<<endl;
    }
return 0;
 }

OUTPUT

Enter number: 6

1x1=1   1x2=2   1x3=3   1x4=4   1x5=5   1x6=6
2x1=2   2x2=4   2x3=6   2x4=8   2x5=10  2x6=12
3x1=3   3x2=6   3x3=9   3x4=12  3x5=15  3x6=18
4x1=4   4x2=8   4x3=12  4x4=16  4x5=20  4x6=24
5x1=5   5x2=10  5x3=15  5x4=20  5x5=25  5x6=30
6x1=6   6x2=12  6x3=18  6x4=24  6x5=30  6x6=36
7x1=7   7x2=14  7x3=21  7x4=28  7x5=35  7x6=42
8x1=8   8x2=16  8x3=24  8x4=32  8x5=40  8x6=48
9x1=9   9x2=18  9x3=27  9x4=36  9x5=45  9x6=54
10x1=10 10x2=20 10x3=30 10x4=40 10x5=50 10x6=60

while-loop  with if-else statement in C++

in the below codes, we will print even and odd numbers in differently.

#include<iostream>
using namespace std; 

 int main()
 {
   int count=0,even=0,odd=0,size=11;
   cout<<"even"<<"\t"<<"odd"<<endl;

   while(count<=size)
    {
//while body
      if(count%2==0) {
	     cout<<count<<"\t";
	     even+=count; //sum of even
	  }

      else    {
	     cout<<count<<"\n";
	     odd+=count; //sum of odd
	   }

      count++;
   }
   cout<<"____________\n";
   cout<<even<<"\t"<<odd;
return 0;
}

OUTPUT

even    odd
0       1
2       3
4       5 
6       7
8       9
10      11 
____________
30      36

for-loop and while-loop, both are similar. C++ also provides a different loop is called the do-while loop.

Related Exercise

• Print Fibonacci Series in C++
• Print large form Table in C++

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