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Loops in C

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Loops are fundamental constructs in programming that allow you to execute a block of code repeatedly based on a condition. In C, there are three primary types of loops:

  1. For Loop
  2. While Loop
  3. Do-While Loop

Each type of loop serves a specific purpose and can be used in different scenarios. Let's explore each one in detail.

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 <stdio.h>

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

Explanation

  • Initialization: int i = 0; initializes the loop variable i to 0.
  • Condition: i < 5; checks if i is less than 5. If true, the loop continues; otherwise, it stops.
  • Increment/Decrement: i++ increments i by 1 after each iteration.

Practical Exercise

Task: Write a for loop that prints the first 10 even numbers.

Solution:

#include <stdio.h>

int main() {
    int i;
    for (i = 0; i < 20; i += 2) {
        printf("%d\n", i);
    }
    return 0;
}

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 <stdio.h>

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

Explanation

  • Condition: i < 5; checks if i is less than 5. If true, the loop continues; otherwise, it stops.
  • Increment/Decrement: i++ increments i by 1 after each iteration.

Practical Exercise

Task: Write a while loop that prints numbers from 10 to 1.

Solution:

#include <stdio.h>

int main() {
    int i = 10;
    while (i > 0) {
        printf("%d\n", i);
        i--;
    }
    return 0;
}

Do-While Loop

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

Syntax

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

Example

#include <stdio.h>

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

Explanation

  • Code Block: The code inside the do block is executed first.
  • Condition: i < 5; checks if i is less than 5. If true, the loop continues; otherwise, it stops.

Practical Exercise

Task: Write a do-while loop that prints the numbers from 1 to 5.

Solution:

#include <stdio.h>

int main() {
    int i = 1;
    do {
        printf("%d\n", i);
        i++;
    } while (i <= 5);
    return 0;
}

Common Mistakes and Tips

  1. Infinite Loops: Ensure that the loop condition will eventually become false. Otherwise, the loop will run indefinitely.

    • Example of an infinite loop: 
      while (1) {
    // This loop will run forever
}

  2. Off-by-One Errors: Be careful with the loop boundaries to avoid executing the loop one time too many or too few.

    • Example: 
      for (int i = 0; i <= 5; i++) {
    // This loop runs 6 times, not 5
}

  3. Proper Initialization and Increment/Decrement: Ensure that the loop variable is correctly initialized and updated to avoid unexpected behavior.

Conclusion

In this section, we covered the three primary types of loops in C: for, while, and do-while. Each loop type has its specific use cases and syntax. Understanding how to use these loops effectively is crucial for controlling the flow of your programs. Practice writing different types of loops to become more comfortable with their syntax and behavior. In the next section, we will explore the switch statement, which provides an alternative to using multiple if-else statements.

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