Loops allow programmers to execute a block of code multiple times without needing to write the same code repeatedly. The three primary types of loops in C are:

• for loop
• while loop
• do-while loop

Each of these loops serves different use cases and has specific syntax rules.

The for Loop

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

Syntax

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

Components

• Initialization: This is executed once at the beginning of the loop. It usually involves declaring and initializing loop control variables.
• Condition: Before each iteration, this expression is evaluated. If it evaluates to true (non-zero), the loop body executes; otherwise, the loop terminates.
• Increment/Decrement: This expression updates the loop control variable at the end of each iteration.

Example

#include <stdio.h>

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

Output:

Iteration 0
Iteration 1
Iteration 2
Iteration 3
Iteration 4

The while Loop

The while loop is used when the number of iterations is not known in advance. The loop continues as long as the specified condition is true.

Syntax

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

Example

#include <stdio.h>

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

Output:

Count: 0
Count: 1
Count: 2
Count: 3
Count: 4

The do-while Loop

The do-while loop is similar to the while loop, except that it guarantees at least one execution of the loop body since the condition is checked after the loop body.

Syntax

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

Example

#include <stdio.h>

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

Output:

Count: 0
Count: 1
Count: 2
Count: 3
Count: 4

Loop Control Statements

In addition to the basic looping constructs, C provides several control statements to manipulate loop execution:

• break: Terminates the loop immediately.

  for (int i = 0; i < 10; i++) {
      if (i == 5) {
          break; // exits loop when i is 5
      }
      printf("%d\n", i);
  }
  

• continue: Skips the current iteration and moves to the next one.

  for (int i = 0; i < 10; i++) {
      if (i % 2 == 0) {
          continue; // skips even numbers
      }
      printf("%d\n", i);
  }
  

Nesting Loops

Loops can be nested within each other. However, care should be taken to manage performance and ensure that termination conditions are met to avoid infinite loops.

Example of Nested Loops

#include <stdio.h>

int main() {
    for (int i = 1; i <= 3; i++) {
        for (int j = 1; j <= 2; j++) {
            printf("i: %d, j: %d\n", i, j);
        }
    }
    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

Summary

Loops are an essential feature that allow programmers to efficiently manage repetitive tasks.

Understanding the syntax and structure of for, while, and do-while loops, along with loop control statements like break and continue, is vital for effective programming.