Days 3-4: Flow Control and Functions

Objective:

• Learn if-else, loops (for, while, do-while), and switch-case.

• Create simple examples to understand flow control.

• Learn to create and call functions.

---

1. Flow Control

1.1 If-Else Statements:

The if-else statement is used to execute code blocks based on a condition.

void main() {
  int number = 10;

  if (number > 0) {
    print('$number is positive');
  } else if (number < 0) {
    print('$number is negative');
  } else {
    print('$number is zero');
  }
}

Explanation:

• The program checks if the number is greater than, less than, or equal to zero and prints the appropriate message.

1.2 Loops:

For Loop: The for loop is used to repeat a block of code a fixed number of times.

void main() {
  for (int i = 0; i < 5; i++) {
    print('i = $i');
  }
}

Explanation:

• The loop starts from i = 0 and runs until i < 5, incrementing i by 1 in each iteration.

While Loop: The while loop is used to repeat a block of code as long as a condition is true.

void main() {
  int i = 0;

  while (i < 5) {
    print('i = $i');
    i++;
  }
}

Explanation:

• The loop runs as long as i < 5 and increments i in each iteration.

Do-While Loop: The do-while loop is similar to the while loop but guarantees at least one iteration.

void main() {
  int i = 0;

  do {
    print('i = $i');
    i++;
  } while (i < 5);
}

Explanation:

• The loop runs at least once and continues as long as i < 5.

1.3 Switch-Case Statement:

The switch-case statement is used to execute one code block among many based on the value of a variable.

void main() {
  int day = 3;

  switch (day) {
    case 1:
      print('Monday');
      break;
    case 2:
      print('Tuesday');
      break;
    case 3:
      print('Wednesday');
      break;
    case 4:
      print('Thursday');
      break;
    case 5:
      print('Friday');
      break;
    case 6:
      print('Saturday');
      break;
    case 7:
      print('Sunday');
      break;
    default:
      print('Invalid day');
  }
}

Explanation:

• The switch statement evaluates the value of day and executes the matching case.

---

2. Functions

Functions are reusable blocks of code that perform a specific task.

2.1 Defining and Calling Functions:

void greet(String name) {
  print('Hello, $name!');
}

void main() {
  greet('Alice');
  greet('Bob');
}

Explanation:

• The greet function takes a String parameter and prints a greeting message.

• The main function calls greet with different arguments.

2.2 Returning Values from Functions:

int add(int a, int b) {
  return a + b;
}

void main() {
  int sum = add(3, 5);
  print('Sum: $sum');
}

Explanation:

• The add function takes two int parameters and returns their sum.

• The main function calls add and prints the result.

2.3 Anonymous Functions:

Anonymous functions are functions without a name, often used for short operations.

void main() {
  List<int> numbers = [1, 2, 3, 4, 5];

  numbers.forEach((number) {
    print(number);
  });
}

Explanation:

• The forEach method takes an anonymous function and applies it to each element in the list.

---

Examples with Explanations

Example 1: Using If-Else and Loops

void main() {
  int number = 5;

  if (number % 2 == 0) {
    print('$number is even');
  } else {
    print('$number is odd');
  }

  for (int i = 1; i <= 10; i++) {
    print('$number x $i = ${number * i}');
  }
}

Explanation:

• The program checks if the number is even or odd and prints the result.

• It then prints the multiplication table for the number using a for loop.

Example 2: Switch-Case with Functions

String getDayName(int day) {
  switch (day) {
    case 1:
      return 'Monday';
    case 2:
      return 'Tuesday';
    case 3:
      return 'Wednesday';
    case 4:
      return 'Thursday';
    case 5:
      return 'Friday';
    case 6:
      return 'Saturday';
    case 7:
      return 'Sunday';
    default:
      return 'Invalid day';
  }
}

void main() {
  int day = 4;
  print('Day $day is ${getDayName(day)}');
}

Explanation:

• The getDayName function takes a day number and returns the corresponding day name using a switch-case statement.

• The main function calls getDayName and prints the result.

---

Visual Explanations

1. If-Else Statement:

• Figure 1.1: Flowchart of an if-else statement.

  

• Figure 1.2: Example of using if-else statement in Dart.

  

2. For Loop:

• Figure 2.1: Flowchart of a for loop.

  

• Figure 2.2: Example of using for loop in Dart.

  

3. While Loop:

• Figure 3.1: Flowchart of a while loop.

  

• Figure 3.2: Example of using while loop in Dart.

  

4. Do-While Loop:

• Figure 4.1: Flowchart of a do-while loop.

  

• Figure 4.2: Example of using do-while loop in Dart.

  

5. Switch-Case Statement:

• Figure 5.1: Flowchart of a switch-case statement.

  

• Figure 5.2: Example of using switch-case statement in Dart.

  

6. Functions:

• Figure 6.1: Diagram of a function call.

  

• Figure 6.2: Example of using function call in Dart.

  

By following this guide, you'll have a solid understanding of flow control statements and functions in Dart, enabling you to write more complex and efficient programs. Happy coding!