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Loops

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Loops are fundamental constructs in programming that allow you to execute a block of code multiple times. In C++, there are three primary types of loops: for, while, and do-while. Each type of loop serves different purposes and is used in different scenarios.

Types of Loops

  1. for Loop

The for loop is used when the number of iterations is known beforehand. It consists of three parts: initialization, condition, and increment/decrement.

Syntax:

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

Example:

#include <iostream>
using namespace std;

int main() {
    for (int i = 0; i < 5; i++) {
        cout << "Iteration " << i << endl;
    }
    return 0;
}

Explanation:

  • Initialization: int i = 0 sets the starting point.
  • Condition: i < 5 checks if the loop should continue.
  • Increment/Decrement: i++ updates the loop variable.

  1. while Loop

The while loop is used when the number of iterations is not known beforehand. It continues to execute as long as the condition is true.

Syntax:

while (condition) {
    // Code to be executed
}

Example:

#include <iostream>
using namespace std;

int main() {
    int i = 0;
    while (i < 5) {
        cout << "Iteration " << i << endl;
        i++;
    }
    return 0;
}

Explanation:

  • Condition: i < 5 checks if the loop should continue.
  • Increment/Decrement: i++ updates the loop variable inside the loop body.

  1. do-while Loop

The do-while loop is similar to the while loop, but it guarantees that the loop body is executed at least once.

Syntax:

do {
    // Code to be executed
} while (condition);

Example:

#include <iostream>
using namespace std;

int main() {
    int i = 0;
    do {
        cout << "Iteration " << i << endl;
        i++;
    } while (i < 5);
    return 0;
}

Explanation:

  • Loop Body: The code inside the do block is executed first.
  • Condition: i < 5 checks if the loop should continue.

Practical Exercises

Exercise 1: Sum of First N Natural Numbers

Problem: Write a program to calculate the sum of the first N natural numbers using a for loop.

Solution:

#include <iostream>
using namespace std;

int main() {
    int N, sum = 0;
    cout << "Enter a positive integer: ";
    cin >> N;

    for (int i = 1; i <= N; i++) {
        sum += i;
    }

    cout << "Sum of first " << N << " natural numbers is: " << sum << endl;
    return 0;
}

Exercise 2: Factorial of a Number

Problem: Write a program to calculate the factorial of a number using a while loop.

Solution:

#include <iostream>
using namespace std;

int main() {
    int N, factorial = 1;
    cout << "Enter a positive integer: ";
    cin >> N;

    int i = 1;
    while (i <= N) {
        factorial *= i;
        i++;
    }

    cout << "Factorial of " << N << " is: " << factorial << endl;
    return 0;
}

Exercise 3: Reverse a Number

Problem: Write a program to reverse a number using a do-while loop.

Solution:

#include <iostream>
using namespace std;

int main() {
    int num, reversedNum = 0;
    cout << "Enter an integer: ";
    cin >> num;

    do {
        int digit = num % 10;
        reversedNum = reversedNum * 10 + digit;
        num /= 10;
    } while (num != 0);

    cout << "Reversed number is: " << reversedNum << endl;
    return 0;
}

Common Mistakes and Tips

  • Infinite Loops: Ensure that the loop condition will eventually become false. Otherwise, the loop will run indefinitely.
  • Off-by-One Errors: Be careful with the loop boundaries to avoid executing the loop one time too many or too few.
  • Initialization and Update: Properly initialize and update the loop variable to avoid logic errors.

Conclusion

In this section, we covered the three primary types of loops in C++: for, while, and do-while. We discussed their syntax, provided practical examples, and included exercises to reinforce the concepts. Understanding loops is crucial for controlling the flow of your programs and performing repetitive tasks efficiently. In the next section, we will explore the switch case statement, which provides an alternative to using multiple if-else statements.

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