Conditions in Dart

Here's a very detailed introduction to if, else, else if, ternary operator (? :), and switch statements in Dart using DartPad, with solved and unsolved problems for practice.

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🧠 Introduction to Decision-Making in Dart

In programming, decision-making allows your program to take different paths based on conditions. Dart provides several ways to perform this:

1. if

2. else if and else

3. Ternary Operator (condition ? trueResult : falseResult)

4. switch statement

We'll explain each in simple English, give syntax, examples, and visuals, and provide problems at the end.

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🧩 1. if Statement

Used to execute code only when a condition is true.

📦 Syntax

if (condition) {
  // code if condition is true
}

✅ Example

void main() {
  int age = 20;
  if (age >= 18) {
    print('You are an adult.');
  }
}

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🧩 2. else and else if

Used when you want to provide alternative paths.

📦 Syntax

if (condition1) {
  // true block
} else if (condition2) {
  // another condition
} else {
  // default
}

✅ Example

void main() {
  int marks = 65;
  if (marks >= 90) {
    print('Grade: A');
  } else if (marks >= 75) {
    print('Grade: B');
  } else if (marks >= 60) {
    print('Grade: C');
  } else {
    print('Fail');
  }
}

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🧩 3. Ternary Operator

Used for shorter if-else logic when assigning or returning values.

📦 Syntax

condition ? valueIfTrue : valueIfFalse;

✅ Example

void main() {
  int age = 16;
  String type = (age >= 18) ? 'Adult' : 'Minor';
  print(type); // Output: Minor
}

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🧩 4. switch Statement

Useful when comparing a single value against multiple constant cases.

📦 Syntax

switch (variable) {
  case value1:
    // code
    break;
  case value2:
    // code
    break;
  default:
    // default code
}

✅ Example

void main() {
  String grade = 'B';
  switch (grade) {
    case 'A':
      print('Excellent');
      break;
    case 'B':
      print('Good');
      break;
    case 'C':
      print('Average');
      break;
    default:
      print('Fail or Unknown grade');
  }
}

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🎯 DartPad Practice

Use this link to try: https://dartpad.dev

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🧠 Solved Problems

1. Check if a number is positive, negative, or zero

void main() {
  int num = 0;
  if (num > 0) {
    print('Positive');
  } else if (num < 0) {
    print('Negative');
  } else {
    print('Zero');
  }
}

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2. Find the largest of three numbers

void main() {
  int a = 10, b = 25, c = 15;
  if (a >= b && a >= c) {
    print('$a is the largest');
  } else if (b >= a && b >= c) {
    print('$b is the largest');
  } else {
    print('$c is the largest');
  }
}

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3. Use a switch to print day name from number (1-7)

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');
  }
}

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❓ Unsolved Practice Problems (Try in DartPad)

1. Write a program that checks if a year is a leap year.

Hint: Leap year if divisible by 4 and (not divisible by 100 or divisible by 400).

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2. Accept a number and print if it's even or odd using ternary operator.

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3. Based on temperature input, print:

• "Cold" if < 15

• "Warm" if 15–30

• "Hot" if > 30

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4. Use a switch to display months with 31, 30, or 28/29 days. Input is month name.

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5. Ask for marks and print:

• 90+ → Excellent

• 75-89 → Good

• 60-74 → Average

• below 60 → Needs Improvement

Use if-else if.

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