Understanding While Loop in C++

While Loop in C++

It repeatedly carries out a series of instructions till a condition is true. It is an entry-controlled loop. The while loop in C++ is used when we don’t know the number of iterations.

Syntax

while(testCondition){ 
//code to be executed 
} 

If the testCondition inside the () becomes true, the body of the loop executes else loop terminates without execution. The process repeats until the testCondition becomes false.

Example to demonstrate while loop in C++

 #include <iostream>
using namespace std;
int main() {
 int i = 1;
 while (i <= 10) {
 cout << i << endl;
 i++;
 }
 return 0;
}

• In the above code in C++ Compiler, i is initialized to 1 before the start of the loop.
• The testCondition, i<=10 is evaluated. If true, the body of the loop executes.
• If the condition becomes false in the beginning itself, the program control does not even enter the loop once.
• The loop executes until i becomes 10.

Output

1
2
3
4
5
6
7
8
9
10

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Nested While Loop in C++

Example to demonstrate Nested do...while loop in C++

 #include <iostream>
using namespace std;
int main() {
 int i = 1, j = 1;
 while (i <= 3) {
 cout << "Outer loop iteration " << i << endl;
 while (j <= 3) {
 cout << " Inner loop iteration " << j << endl;
 j++;
 }
 j = 1; // reset j to 1 for the next iteration of the outer loop
 i++;
 }
 return 0;
}

• The inner loop j iterates within each iteration of the outer loop i, printing "Inner loop iteration" messages
• The outer loop i iterates three times, printing "Outer loop iteration" messages.
• After each inner loop is finished, j is reset to 1, resulting in nested iteration.

Output

Outer loop iteration 1
 Inner loop iteration 1
 Inner loop iteration 2
 Inner loop iteration 3
Outer loop iteration 2
 Inner loop iteration 1
 Inner loop iteration 2
 Inner loop iteration 3
Outer loop iteration 3
 Inner loop iteration 1
 Inner loop iteration 2
 Inner loop iteration 3

Infinite while loop in C++

Syntax

while(true) 
{ 
 // body of the loop.. 
} 

Example to demonstrate infinite do...while loop in C++

#include <iostream>
using namespace std;
int main() {
 char str[] = "Infinite while loop";
 int i = 0;

 while (true) {
 i++;
 cout << "i is: " << i << endl;
 }

 // The return statement may never be reached in an infinite loop.
 return 0;
}

Here, the value of i will be printed n number of times due to the absence of a terminating condition.

Output

i is: 1
i is: 2
i is: 3
i is: 4
i is: 5
... 

Summary