C++ Loop Types: An Easy Guide

Introduction

In C++, there are situations where you need to do something over and over again, maybe many times. Loops are like a helper when you want to repeat a set of actions multiple times. They let you run a group of commands repeatedly. They allow our programs to repeat a set of instructions until a specific condition is satisfied. This helps us automate tasks and make our programs more efficient. In this article, we will explore different types of loops, their purpose, and how to use them effectively. So get ready to level up your programming skills with loops!

What Are Loops in C++?

There are mainly two types of loops:  

1. Entry Controlled Loops: In this type of loop, the test condition is tested before entering the loop body. For Loop and While Loop is entry-controlled loops.
2. Exit Controlled Loops: In this type of loop the test condition is tested or evaluated at the end of the loop body. Therefore, the loop body will execute at least once, irrespective of whether the test condition is true or false. the do-while loop is exit controlled loop.

In C++, loops are used to repeat a block of code multiple times. They help in automating repetitive tasks, making your code more efficient. There are three main types of loops in C++: the ‘for‘ loop, the ‘while‘ loop, and the ‘do-while‘ loop. Let’s break down each of them:

• For Loop: The ‘for‘ loop is ideal when you know the number of iterations beforehand. It consists of three parts: initialization, condition, and increment/decrement. The loop executes as long as the condition is true.

• While Loop: The ‘while‘ loop is useful when you don’t know the exact number of iterations beforehand. It repeats as long as the specified condition is true. You need to make sure the condition eventually becomes false to prevent an infinite loop.

• Do-While Loop: Similar to the ‘while‘ loop, the do-while loop executes a block of code while the condition is true. The key difference is that the code block is executed at least once, regardless of whether the condition is true or false.

How Are Loops Used in C++?

For Loop:

In C++, the ‘for‘ loop is used when we know the exact number of times a block of code needs to be executed. It allows us to specify the initialization, condition, and increment/decrement in one line.

Here’s the basic syntax of a ‘for‘ loop in C++:

for (initialization; condition; increment/decrement)
{
    // code block to be executed
}

Here’s what the different parts do:

1. Initialization: This step is where we initialize our counter to a starting value. This part runs only once.
2. Condition: In this step, we test the condition. If it’s true, the code block within the loop is executed. If it’s false, the code block is ignored, and the loop ends.
3. Increment/Decrement: This is the part where we increase or decrease our counter.

Code Example:

#include<iostream>
using namespace std;

int main() {
    for(int i=0; i<5; i++) {
        cout << "The value of i is: " << i << endl;
    }
    return 0;
}

Output:

The value of i is: 0
The value of i is: 1
The value of i is: 2
The value of i is: 3
The value of i is: 4

Explanation:

• Initialization (i=0): We start by setting the value of ‘i’ to 0.
• Condition (i<5): The loop will continue as long as ‘i’ is less than 5.
• Increment (i++): After each iteration, we increase the value of ‘i’ by one.

This is because the loop runs from ‘i=0‘ to ‘i=4‘ (i.e., 5 times), and each time it prints the current value of ‘i‘. After the value of ‘i‘ becomes 5, the condition i<5 is no longer true, so the loop ends.

While Loop

In C++, a “while” loop is a fundamental concept that helps us perform a set of instructions repeatedly as long as a certain condition is true. When that condition becomes false, the loop stops and the program continues with the code that follows the loop.

Syntax:

while (specific condition) {
    // Tasks to do while condition is true
}

The ‘specific condition‘ is a test that results in either true or false. If true, the tasks inside the loop are executed. If false, the loop halts.

Code Example:

#include <iostream>

int main() {
    int tick = 0;

    while (tick < 5) {
        std::cout << "Tick number: " << tick << std::endl;
        tick++;
    }

    return 0;
}

What’s happening in this Code?

• First, we incorporate the iostream library to enable input and output operations.
• Then, we define our ‘main‘ function which serves as the entry point for our program.
• Inside the ‘main‘ function, we initiate a variable named ‘tick‘ and set it to 0.
• Next, we’ve got our while loop. The loop will continue as long as ‘tick‘ is less than 5.
• Within the loop, we print the current value of the ‘tick‘ and then increase ‘tick‘ by one.
• As soon as ‘tick‘ becomes equal to 5, the loop condition ‘tick < 5‘ turns false, and the loop ends.
• Lastly, the ‘main‘ function returns 0 which signals that everything went smoothly.

Output:

Tick number: 0
Tick number: 1
Tick number: 2
Tick number: 3
Tick number: 4

So, each time the loop runs, ‘tick‘ increases by one and its value is displayed. This continues until ‘tick‘ is no longer less than 5, at which point the loop’s condition is no longer true, and the loop finishes.

Do-While Loop

The “do-while” loop in C++ is a way to repeat a set of actions. Unlike other loops, it checks the condition after doing the actions, so the actions are performed at least once. This loop is like a guarantee that something will happen before checking if it should continue. It’s like saying, “Do this, and then see if you should do it again.” This can be useful when you want to make sure a piece of code runs no matter what, and then decide whether it should run again based on a condition.

Here is the syntax:

do {
   // Statements
} while(condition);

First, the block of code within the ‘do {}‘ section is executed. Then, the program checks the ‘while(condition)‘ part. If the condition is true, the loop is executed again. This repeats until the condition becomes false.

Code Example:

#include<iostream>
using namespace std;

int main() {
    int num = 1;

    do {
        cout << "Number: " << num << endl;
        num++;
    } while(num <= 5);

    return 0;
}

Code Explanation:

• An integer variable ‘num‘ is declared and initialized to 1.
• The ‘do-while‘ loop is used.
• Inside the loop, the current value of ‘num‘ is printed.
• The value of ‘num‘ is then incremented by one.
• The loop continues as long as ‘num‘ is less than or equal to 5.

Output:

Number: 1
Number: 2
Number: 3
Number: 4
Number: 5

Even if the initial value of ‘num‘ was set to a number greater than 5, say 6, the loop would still print “Number: 6” once because the ‘do-while‘ loop guarantees the code inside gets executed at least once before checking the condition.

Remember to use the ‘do-while‘ loop when you want to execute the loop body at least once, regardless of the condition.

Real-life Scenarios

Let’s take a look at a real-world example where we might use a loop in C++: managing a digital inventory system for a bookstore.

Here’s the scenario:

Imagine you’re a bookstore owner and you have a digital system to track your inventory. You want to regularly check the number of books in your stock and if the count of any book goes below a certain threshold, let’s say 10, you’d want to order more.

The inventory could be represented in a program as an array (or a list) where each element corresponds to the count of a particular book. You could use a ‘for‘ loop to iterate over this array and check each book’s stock level. Here’s a simple representation:

#include<iostream>
using namespace std;

int main() {
    // Array of books inventory, each element represents a book's count.
    int inventory[5] = {5, 10, 7, 12, 9};

    // We iterate over each book.
    for (int i = 0; i < 5; i++) {
        // Check if book count is below threshold.
        if (inventory[i] < 10) {
            cout << "Book " << i+1 << " is below threshold. Need to order more." << endl;
        }
    }

    return 0;
}

Output:

Book 1 is below threshold. Need to order more.
Book 3 is below threshold. Need to order more.
Book 5 is below threshold. Need to order more.

Explanation:

• The code has an array called “inventory” with 5 elements, representing book stock counts.
• A for loop is used to go through each element in the “inventory” array.
• Inside the loop, an if statement checks if the current book’s stock count is less than 10.
• If the condition is met, a message is printed saying the stock is below the threshold and more should be ordered.

A Problem to Solve

Problem:

You are a math teacher and you have a class of 20 students. Each student has taken a quiz which was graded out of 10 points. You have recorded the scores in a system, and now you want to calculate the average quiz score for the class.

To simplify this task, let’s assume that you have all the scores saved in an array.

Write a C++ program to calculate and print the average score for the class.

Hints:

1. Use a ‘for‘ loop to iterate over the array of scores.
2. Keep a running total of all the scores.
3. After the loop, divide the total score by the number of students to calculate the average.
4. Print out the average score.

Remember, an average is calculated by adding up all the values in a set and then dividing by the number of values in that set.

Here is an example of how you might initialize your scores array, for the purposes of testing your program:

int scores[20] = {8, 9, 7, 6, 10, 8, 9, 10, 8, 7, 6, 7, 8, 9, 10, 8, 7, 9, 8, 10};

Try solving this problem to get a better understanding of how loops work in C++.

The Pros and Cons of Using Loops

Key Takeaways

• Loops allow us to repeat a block of code multiple times.
• They help automate repetitive tasks, reducing the need for manual repetition.
• By using loops, we can process large data sets or perform complex operations more efficiently.
• Loops enable us to create interactive and dynamic programs that respond to user input.
• However, it’s important to avoid infinite loops, as they can cause program crashes.
• Care must be taken to ensure loop conditions are properly defined and updated to prevent unintended behavior.

Conclusion

In summary, loops in C++ are like magic wands that make your code smarter and faster. They help do the same job again and again without you having to write it out each time. The better you get at using loops, the easier it is to make cool and efficient programs. So, keep practicing with loops, and soon, you’ll be an expert at making your code do awesome things!

FAQs

• What are loops in C++?
  Loops in C++ are a way for us to repeat a block of code. There are three types of loops in C++: for, while, and do-while.
• Why do we use loops in C++?
  We use loops in C++ to make our programs more efficient and interactive. They allow our programs to do something over and over again until a certain condition is met.
• How do we use loops in C++?
  We use loops in C++ by using for, while, and do-while statements to control the flow of our program.
• Can using loops make code more confusing?
  Yes, if you use loops incorrectly, it can lead to problems like infinite loops or off-by-one errors. It’s important to understand how loops work and when to use them.

5. What are some examples of using loops in C++?
   Some examples include using for, while, and do-while loops to control the flow of a program based on different conditions.