Loops in C:

In the world of programming, loops are essential for executing a block of code repeatedly. One of the most commonly used loops in C is the `for` loop. This blog post will dive deep into `for` loops in C, explaining their structure, usage, and providing practical examples.

#### What is a `for` Loop?

A `for` loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. It is especially useful when the number of iterations is known beforehand. The general syntax of a `for` loop in C is:

```c

for (initialization; condition; increment) {

// code to be executed

}

```

Let's break down the components:

- **Initialization**: Sets up the loop counter.

- **Condition**: Evaluated before each iteration. If true, the loop continues; if false, the loop stops.

- **Increment**: Updates the loop counter after each iteration.

#### Basic Example

Here's a simple example that prints numbers from 1 to 10:

```c

#include <stdio.h>

int main() {

for (int i = 1; i <= 10; i++) {

printf("%d\n", i);

}

return 0;

}

```

In this example:

- The loop starts with `i` set to 1.

- It continues to run as long as `i` is less than or equal to 10.

- After each iteration, `i` is incremented by 1.

#### Looping Through Arrays

`for` loops are particularly useful for iterating over arrays. Let's see how we can use a `for` loop to print the elements of an array:

```c

#include <stdio.h>

int main() {

int numbers[] = {10, 20, 30, 40, 50};

int size = sizeof(numbers) / sizeof(numbers[0]);

for (int i = 0; i < size; i++) {

printf("Element at index %d: %d\n", i, numbers[i]);

}

return 0;

}

```

Here, the loop runs from 0 to the size of the array minus one, printing each element.

#### Nested `for` Loops

You can also nest `for` loops inside each other. This is particularly useful for working with multi-dimensional arrays or creating patterns. For example, let's print a multiplication table:

```c

#include <stdio.h>

int main() {

for (int i = 1; i <= 10; i++) {

for (int j = 1; j <= 10; j++) {

printf("%4d", i * j);

}

printf("\n");

}

return 0;

}

```

In this example, the outer loop iterates through numbers 1 to 10, and for each iteration, the inner loop also iterates through numbers 1 to 10, printing the product of `i` and `j`.

#### Controlling Loop Execution

Sometimes, you might want to skip an iteration or exit the loop early. You can achieve this using `continue` and `break` statements.

- **`continue`**: Skips the rest of the current iteration and proceeds with the next iteration.

- **`break`**: Exits the loop immediately.

Here’s an example demonstrating both:

```c

#include <stdio.h>

int main() {

for (int i = 1; i <= 10; i++) {

if (i == 5) {

continue; // skip the rest of the loop when i is 5

}

if (i == 8) {

break; // exit the loop when i is 8

}

printf("%d\n", i);

}

return 0;

}

```

Output:

```

In this code:

- When `i` is 5, the `continue` statement skips the `printf` and proceeds to the next iteration.

- When `i` is 8, the `break` statement exits the loop.

Here are five programming problems that focus on using `for` loops in C:

### Problem 1: Sum of Even Numbers

Write a program that calculates the sum of all even numbers from 1 to 100.

**Example Output:**

```

Sum of even numbers from 1 to 100 is: 2550

```

### Problem 2: Factorial Calculation

Write a program that calculates the factorial of a given positive integer. The program should prompt the user to enter a number, and then print the factorial of that number.

**Example Input:**

```

Enter a number: 5

```

**Example Output:**

```

Factorial of 5 is: 120

```

### Problem 3: Reverse an Array

Write a program that reverses the elements of an array. The program should define an array of integers, print the original array, reverse the array using a `for` loop, and then print the reversed array.

**Example Output:**

```

Original array: 1 2 3 4 5

Reversed array: 5 4 3 2 1

```

### Problem 4: Prime Numbers

Write a program that prints all prime numbers between 1 and 100. A prime number is a number greater than 1 that has no divisors other than 1 and itself.

**Example Output:**

```

Prime numbers between 1 and 100: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97

```

### Problem 5: Multiplication Table

Write a program that generates a multiplication table for numbers 1 through 10. The program should use nested `for` loops to create a table in a formatted way.

**Example Output:**

```

1 2 3 4 5 6 7 8 9 10

2 4 6 8 10 12 14 16 18 20

3 6 9 12 15 18 21 24 27 30

4 8 12 16 20 24 28 32 36 40

5 10 15 20 25 30 35 40 45 50

6 12 18 24 30 36 42 48 54 60

7 14 21 28 35 42 49 56 63 70

8 16 24 32 40 48 56 64 72 80

9 18 27 36 45 54 63 72 81 90

10 20 30 40 50 60 70 80 90 100