Entry Controlled Loop vs Exit Controlled Loop in C

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Entry Controlled Loop vs Exit Controlled Loop in C

In this article, I will discuss the Differences Between an Entry-Controlled Loop and an Exit-Controlled Loop in C Language with Examples. Please read our previous articles discussing the Nested For loop in C Language with Examples.

Entry Controlled Loop vs Exit Controlled Loop in C

In C programming, loops are used to repeatedly execute a set of statements. Two common types of loops are Entry Controlled Loops and Exit Controlled Loops, each with distinct characteristics.

Entry Controlled Loop in C Language:

An Entry Controlled Loop checks the condition before entering the loop body. The loop body is not executed even once if the condition is false. The most common entry-controlled loop in C is the for loop and the while loop.

  • Example: for loop and while loop.
  • Working Mechanism: The condition is checked before entering the loop body. If the condition is false initially, the loop body is not executed even once.
  • Usage: These loops are used when the number of iterations is known beforehand or when it’s necessary to check the condition before executing the loop body.
Example of for Loop:
#include <stdio.h>

int main() {
    for(int i = 0; i < 5; i++) {
        printf("%d ", i);
    }
    return 0;
}

In this example, the loop will print numbers from 0 to 4. The condition i < 5 is checked before entering the loop.

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Example of while Loop:
#include <stdio.h>

int main() {
    int i = 0;
    while(i < 5) {
        printf("%d ", i);
        i++;
    }
    return 0;
}

Like the for loop, the condition i < 5 is checked before each iteration.

The Behavior of Entry-Controlled Loop:
  • Initialization: Typically, initialization of the loop variable is done before the loop starts.
  • Condition Checking: The condition is checked before the execution of the loop body.
  • Execution: If the condition is true, the loop body is executed. If it’s false, the loop is skipped entirely.
Advantages of Entry-Controlled Loop:
  • Prevents the loop body from executing if the condition is false from the beginning.
  • More straightforward in terms of readability and understanding, especially in scenarios where the initial condition is crucial for the loop execution.
  • Best used when the number of iterations is known beforehand or when it’s necessary to check the condition before executing the loop body.

Exit Controlled Loop in C Language:

In an Exit Controlled Loop, the condition is checked after executing the loop statements. This means the loop body will be executed at least once, regardless of whether the condition is true or false. The do-while loop is an exit-controlled loop in C.

  • Example: do-while loop.
  • Working Mechanism: The condition is checked after executing the loop body. Therefore, the loop body is executed at least once, regardless of whether the condition is true or false.
  • Usage: This loop is preferable when the loop body needs to be executed at least once, such as in menu-driven programs where a menu is displayed and the condition is checked.
Example of a do-while Loop:
#include <stdio.h>

int main() {
    int i = 0;
    do {
        printf("%d ", i);
        i++;
    } while(i < 5);
    return 0;
}

The loop will also print numbers from 0 to 4 in this example. However, the key difference is that the condition i < 5 is checked after the loop body is executed.

The Behavior of Exit-Controlled Loop:
  • Initialization: Like entry-controlled loops, initialization usually occurs before the loop.
  • Execution: The loop body is executed first.
  • Condition Checking: After the loop body is executed, the condition is checked. If true, the loop continues; if false, the loop ends.
Advantages of Exit Controlled Loop:
  • Ensures that the loop body is executed at least once.
  • It is useful in scenarios where the initial iteration needs to happen without condition checking, like initializing a process or displaying a menu.
  • Ideal for situations where the loop must be executed at least once, such as when the loop body initializes or modifies the condition variable.
Key Differences Between Entry Controlled Loop vs Exit Controlled Loop in C:
  • Initiation of Loop: In entry-controlled loops, condition checking is done at the start, while in exit-controlled loops, it’s done at the end.
  • Condition Checking: The condition is checked before the loop body is executed in Entry Controlled Loops. Exit Controlled Loops check the condition after the loop body is executed.
  • Guaranteed Execution: Exit-controlled loops guarantee at least one execution of the loop body, whereas entry-controlled loops do not.
  • Use Case: Entry-controlled loops are chosen when the initial condition is crucial, while exit-controlled loops are chosen when at least one execution is required, regardless of the condition.

In summary, the main difference lies in when the condition is checked: before the loop body in entry-controlled loops (for, while) and after the loop body in exit-controlled loops (do-while). This affects how often the loop body is executed, especially in cases where the loop condition is false from the start.

In the next article, I will discuss Jump Statements in C Language with examples. In this article, I explain the Differences Between Entry-Controlled Loop and Exit-Controlled Loop in C Language with Examples. I hope you enjoy this article on Entry Controlled Loop vs Exit Controlled Loop in C. I would like to have your feedback. Please post your feedback, questions, or comments about this article.

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