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Table of contents
1.
What is Loop?
2.
Entry Control Loop
2.1.
Example Code
2.2.
Output
2.3.
Explanation
3.
Exit Control Loop
3.1.
Example Code
3.2.
Output
3.3.
Explanation
4.
Difference between Entry Control Loop and Exit Control Loop
4.1.
Difference in Code
4.2.
Output
4.3.
Explanation
5.
Frequently Asked Questions
5.1.
What is an entry-controlled loop?
5.2.
What is an exit-controlled loop?
5.3.
What is an example of an exit-controlled loop?
5.4.
What is an example of an entry-controlled loop?
5.5.
Can an entry-controlled loop be converted to an exit-controlled loop and vice versa?
6.
Conclusion
Last Updated: Jun 19, 2024
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Difference between Entry Control Loop and Exit Control Loop

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Loops are an essential part of programming to execute a code block repeatedly. There are different loops in programming languages, but they are generally classified into two categories: Entry Controlled loops and Exit Controlled loops. Both loops serve the same purpose but differ in how they check the loop condition. In entry controlled loop the test condition is checked at the beginning of the loop i.e - while loop Whereas in exit controlled the condition is checked after the statements inside the loop body are executed i.e - do-while loop

Difference between Entry Control Loop and Exit Control Loop

We can improve our code's readability, efficiency, and maintainability by selecting the suitable Loop for a given task.

What is Loop?

In programming, a loop is a control structure that allows us to execute instructions repeatedly. A Loop tells the computer to repeat a particular set of instructions continually until a specific condition meets. Several loops are available in programming languages, but the most common ones are:

  • for loopThis Loop iterates over a fixed set of values or a range of values.
  • while loopThis Loop repeats instructions if a specific condition is met.
  • do-while loopThis Loop is similar to the while loop, but the instructions are executed at least once before the condition is checked.

Based on the flow of loops in the code, they are generally classified into Entry Controlled loops and Exit Controlled loops. For more information on Loops, visit this blog.

Entry Control Loop

An entry-controlled loop is a type of Loop in computer programming that tests the loop condition at the Loop's beginning before executing the Loop's body.

entry control loop
  1. As the program flow reaches an entry-controlled loop, the loop condition is tested before the first iteration of the Loop. 
  2. If the condition meets, then the loop body will be executed. If it does not, the loop body will be skipped entirely, and the program will continue execution from the first statement following the Loop.
  3. After running the loop for required iterations (when the condition is not met), the program exits the loop. 

Some popular entry-controlled loops are for Loopwhile Loop, etc.  

Example Code

#include <bits/stdc++.h>
using namespace std;

int main(){
	for(int x = 0; x<10; x++){
		cout<<x<<" "; 
	}
	return 0;
}

Output

output for entry control

Explanation

In the above code, x is a variable initialized with zero, and the Loop will terminate when x equals ten. So, every value of x will be printed from x=0 till x= 9.

These are useful when we know how many times we need to execute the Loop, as they can simplify and make the code more efficient. They are commonly used for iterating over arrays, lists, and other data structures.

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Exit Control Loop

An exit-controlled loop is a type of Loop in computer programming that tests the loop condition at the end of the Loop after executing the body of the Loop at least once.

exit control loop
  1. As the program flow reaches an exit-controlled loop, the loop body is executed first, and then the loop condition is tested.
  2. If the condition is met, the Loop will continue to run, and the body's code will perform again. If it does not, the Loop will exit, and the program will continue execution from the first statement following the Loop.
  3. After running the loop for required iterations (when the condition is not met), the program exits the loop.

Do-while loop is primarily used in the exit-controlled Loop.

Example Code

#include <bits/stdc++.h>
using namespace std;

int main(){
	int x=0;
	do{
    	cout<<x<<" ";
    	x++;
	} while (x<10);
	return 0;
}

Output

output for exit control

Explanation

In the above code, x is initialized with zero, and as the Loop starts, x=0 is printed, and the condition x<10 is checked. So after printing till x=9, x becomes 10. Here the loop condition will fail as x=10 and not x<10, and the Loop will be executed.

This is used when we want to run the instructions in the Loop's body at least once without writing the code explicitly once again before the Loop's code. Hence, we can save our code from redundancy which is the primary reason for using Loops.

Difference between Entry Control Loop and Exit Control Loop

Here, we will see the difference between an Entry Control Loop and an Exit Control Loop:

Parameter 

Entry Control

Exit Control

Flow of loop

The condition is tested at the beginning of the Loop before the loop body executes.

The condition is tested at the end of the Loop after the loop body is executed at least once.

The number of times the loop is executed

The loop body may not be run if the condition is false.

The loop body runs at least once, even if the condition is false.

Example loops

While Loop, For are some popular Entry Controlled Loops. 

Do-while is usually used as Exit Controlled Loop.

Efficiency

Since the condition is tested at the beginning of the Loop, the loop body's code can be skipped if it is false.

Exit-controlled loops consistently execute the loop body at least once, which can be less efficient if the condition is false.

Application

It is mostly used when we know how many iterations are required and the loop condition is always met. 

It is used when the loop body’s code needs to be executed at least once.

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Difference in Code

This is where we can see the difference between Entry and exit-controlled loops.  

#include <bits/stdc++.h>
using namespace std;

int main(){
	cout<<"Entry controlled loop: ";
	for (int x = 1; x < 1; x++){
        	cout<<x<<" "; 
	}
	cout<<endl;

	cout<<"Exit controlled loop: ";
	int x=1;
	do{
        	cout<<x<<" ";
        	x++;
	} while (x<1);

	return 0;
}

Output

difference in output

Explanation

Here in both Entry and exit loops, x is initialized with 1. Now the terminating condition is x<1 for both. Therefore, the entry loop will not print any output as it first checks the loop condition, but the exit loop will print the value of x as the condition will not be matched. After this, in the exit loop, x becomes 2, greater than 1. Now Loop will be terminated.  

Learn about, Characteristics of OOPS

Frequently Asked Questions

What is an entry-controlled loop?

An entry-controlled loop is a loop where the condition is checked at the beginning of each iteration, and if it is false, the loop body is not executed.

What is an exit-controlled loop?

An exit-controlled loop is a loop where the condition is checked at the end of every iteration, and if it is false, the loop body is not executed.

What is an example of an exit-controlled loop?

do-while loop is an example of an exit-controlled loop. The loop body executes at least once in a do-while loop, and the condition is checked. If it does not meet, the Loop exits; if it does, the Loop continues executing.

What is an example of an entry-controlled loop?

while loop is an example of an entry-controlled loop. In a while loop, the loop condition is checked before the loop body executes, and if it is false, the loop body does not run.

Can an entry-controlled loop be converted to an exit-controlled loop and vice versa?

Yes, it is possible to convert an entry-controlled loop to an exit-controlled loop and vice versa by changing the loop condition and the position of the loop body.

Conclusion

In this article, we briefly discussed loops, Entry Control Loops and Exit Control Loops. We also discussed the difference between Entry Control Loop and Exit Control Loop. They mainly differ in the time of checking the loop condition. Programmers need to understand the difference between Entry Controlled Loops and Exit Controlled Loops, as well as when to use each type of Loop, as this can significantly impact the performance and behaviour of their code.

To learn more about Loops, visit our other blogs:

You may refer to our Guided Path on Code360 to enhance your skill set on DSACompetitive ProgrammingSystem Design, etc. Check out essential interview questions, practice our available mock tests, look at the interview bundle for interview preparations, and so much more!

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