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Loops in Programming

In programming, loops are used to execute a block of code repeatedly until a specific condition is met. Loops are essential for scenarios where you need to perform repetitive tasks, such as traversing arrays, generating patterns, or processing data structures.

Types of Loops​

1. For Loop​

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

Syntax:​

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

Example:​

#include <iostream>
using namespace std;

int main() {
    for (int i = 1; i <= 5; i++) {
        cout << "Iteration " << i << endl;
    }
    return 0;
}

Output:​

Iteration 1
Iteration 2
Iteration 3
Iteration 4
Iteration 5

2. While Loop​

A while loop keeps executing as long as the given condition is true. It is used when the number of iterations is not known in advance.

Syntax:​

while (condition) {
    // Code to execute
}

Example:​

#include <iostream>
using namespace std;

int main() {
    int i = 1;
    while (i <= 5) {
        cout << "Iteration " << i << endl;
        i++;
    }
    return 0;
}

Output:​

Iteration 1
Iteration 2
Iteration 3
Iteration 4
Iteration 5

3. Do-While Loop​

A do-while loop is similar to a while loop, but it guarantees that the code inside the loop will run at least once, even if the condition is false initially.

Syntax:​

do {
    // Code to execute
} while (condition);

Example:​

#include <iostream>
using namespace std;

int main() {
    int i = 1;
    do {
        cout << "Iteration " << i << endl;
        i++;
    } while (i <= 5);
    return 0;
}

Output:​

Iteration 1
Iteration 2
Iteration 3
Iteration 4
Iteration 5

4. Nested Loops​

A nested loop is a loop inside another loop. It is commonly used for tasks like generating patterns or processing 2D arrays.

Example:​

#include <iostream>
using namespace std;

int main() {
    for (int i = 1; i <= 3; i++) {
        for (int j = 1; j <= 2; j++) {
            cout << "i = " << i << ", j = " << j << endl;
        }
    }
    return 0;
}

Output:​

i = 1, j = 1
i = 1, j = 2
i = 2, j = 1
i = 2, j = 2
i = 3, j = 1
i = 3, j = 2

5. Infinite Loops​

An infinite loop is a loop that runs indefinitely because the condition never becomes false.

Example:​

#include <iostream>
using namespace std;

int main() {
    while (true) {
        cout << "This is an infinite loop!" << endl;
        break;  // Add this to avoid an infinite loop
    }
    return 0;
}

Output:​

i = 1, j = 1
i = 1, j = 2
i = 2, j = 1
i = 2, j = 2
i = 3, j = 1
i = 3, j = 2

Loop Control Statements​

1. Break Statement​

The break statement is used to exit a loop prematurely.

Example:​

for (int i = 1; i <= 10; i++) {
    if (i == 5) break;
    cout << i << " ";
}

Output:​

1 2 3 4

1. Continue Statement​

The continue statement is used to skip the current iteration and move to the next iteration of the loop.

Example:​

for (int i = 1; i <= 5; i++) {
    if (i == 3) continue;
    cout << i << " ";
}

Output:​

1 2 4 5

Time Complexity​

For, While, Do-While Loops: Each iteration typically takes O(1) time, so the total time complexity is proportional to the number of iterations, i.e., O(n)for n iterations.

When to Use Each Loop​

  • For Loop: When the number of iterations is known beforehand.
  • While Loop: When the number of iterations is not known and depends on a condition.
  • Do-While Loop: When you need to ensure the loop runs at least once.

Conclusion​

Loops are a fundamental concept in programming, allowing us to perform repetitive tasks efficiently. Knowing which type of loop to use and how to control it with statements like break and continue is essential for writing clean, efficient code.