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Loops

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In programming, loops are used to execute a block of code repeatedly as long as a specified condition is met. Objective-C supports several types of loops, including for, while, and do-while loops. This section will cover each type of loop, provide practical examples, and include exercises to reinforce your understanding.

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:

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        for (int i = 0; i < 5; i++) {
            NSLog(@"Iteration %d", i);
        }
    }
    return 0;
}

Explanation:

  • int i = 0: Initializes the loop counter i to 0.
  • i < 5: The loop runs as long as i is less than 5.
  • i++: Increments i by 1 after each iteration.
  • NSLog(@"Iteration %d", i);: Prints the current value of i.

  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 specified condition is true.

Syntax:

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

Example:

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        int i = 0;
        while (i < 5) {
            NSLog(@"Iteration %d", i);
            i++;
        }
    }
    return 0;
}

Explanation:

  • int i = 0: Initializes the loop counter i to 0.
  • i < 5: The loop runs as long as i is less than 5.
  • NSLog(@"Iteration %d", i);: Prints the current value of i.
  • i++: Increments i by 1 after each iteration.

  1. 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 before the condition is tested.

Syntax:

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

Example:

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        int i = 0;
        do {
            NSLog(@"Iteration %d", i);
            i++;
        } while (i < 5);
    }
    return 0;
}

Explanation:

  • int i = 0: Initializes the loop counter i to 0.
  • NSLog(@"Iteration %d", i);: Prints the current value of i.
  • i++: Increments i by 1 after each iteration.
  • i < 5: The loop runs as long as i is less than 5.

Practical Exercises

Exercise 1: Sum of First 10 Natural Numbers

Task: Write a program to calculate the sum of the first 10 natural numbers using a for loop.

Solution:

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        int sum = 0;
        for (int i = 1; i <= 10; i++) {
            sum += i;
        }
        NSLog(@"Sum of first 10 natural numbers: %d", sum);
    }
    return 0;
}

Exercise 2: Print Even Numbers from 1 to 20

Task: Write a program to print all even numbers from 1 to 20 using a while loop.

Solution:

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        int i = 1;
        while (i <= 20) {
            if (i % 2 == 0) {
                NSLog(@"%d", i);
            }
            i++;
        }
    }
    return 0;
}

Exercise 3: Factorial of a Number

Task: Write a program to calculate the factorial of a number using a do-while loop.

Solution:

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        int number = 5; // Change this value to calculate factorial of a different number
        int factorial = 1;
        int i = 1;
        do {
            factorial *= i;
            i++;
        } while (i <= number);
        NSLog(@"Factorial of %d is %d", number, factorial);
    }
    return 0;
}

Common Mistakes and Tips

  • Off-by-One Errors: Ensure that your loop conditions are correctly set to avoid running the loop one time too many or too few.
  • Infinite Loops: Always make sure that the loop condition will eventually become false. For example, forgetting to increment the loop counter can result in an infinite loop.
  • Initialization and Increment: Properly initialize your loop variables and ensure they are correctly incremented or decremented within the loop.

Conclusion

In this section, you learned about the different types of loops in Objective-C: for, while, and do-while. You also saw practical examples and completed exercises to reinforce your understanding. Loops are a fundamental concept in programming, and mastering them will help you write more efficient and effective code. In the next section, we will explore switch statements, another control flow mechanism in Objective-C.

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