🚀 Dart Cheat Sheet – A Complete Beginner-to-Intermediate Guide

Dart is a modern, object-oriented programming language developed by Google and is primarily used for building Flutter applications. This cheat sheet gives you a clear, structured, and in-depth understanding of Dart’s core concepts, exactly like the screenshot — but with real explanations and examples.

🔹 1. Variables in Dart

Dart supports static typing, but it also provides type inference.

Example:

int n1 = 5;          // explicitly typed
var n2 = 4;          // type inferred as int
dynamic n3 = "abc";  // can change type later

Key Points:

• int, double, String, bool are common types.
• var determines the type at compile time.
• dynamic allows type changes at runtime (use carefully).

n3 = 10; // Valid

🔹 2. Constants (final vs const)

const PI = 3.14;        // compile-time constant
final area = PI * 5 * 5; // runtime constant

Difference:

Use const when value never changes and is known beforehand.

🔹 3. Conditional Expressions

Ternary Operator

var grade = 3;
var result = grade > 3 ? "Cool" : "Not cool";

Null Coalescing Operator

var input;
var age = input ?? 0;

✔ Assigns default value if input is null.

🔹 4. Functions

Standard Function

int addNums(int a, int b, int c) {
  return a + b + c;
}

Calling a Function

print(addNums(1, 2, 3));

🔹 5. Arrow Syntax (Short Functions)

Used for single-expression functions.

void greet() => print("Hello!");

This is cleaner and easier to read.

🔹 6. Optional Positional Parameters

Use square brackets [].

int add(int a, [int b = 0, int c = 0]) {
  return a + b + c;
}

add(1);
add(1, 2);
add(1, 2, 3);

🔹 7. Named Parameters

Named parameters improve readability.

int add({int a = 0, int b = 0, int c = 0}) {
  return a + b + c;
}

add(a: 1, b: 2);

🔹 8. String Interpolation

var name = "World";
print("Hello $name");
print("Sum of 5 and 6 is ${5 + 6}");

✔ Cleaner than string concatenation.

🔹 9. Parsing Strings

int.parse("123");       // 123
double.parse("12.5");   // 12.5

Safe parsing:

int.tryParse("abc"); // null

🔹 10. Lists (Arrays)

var arr = [1, 2, 3, 4, 5];
print(arr.length); // 5
arr[0] = 10;

Add / Remove

arr.add(6);
arr.removeAt(2);

🔹 11. Fixed vs Growable Lists

var fixed = List.filled(3, null);

Fixed-length lists cannot grow.

🔹 12. Maps (Key–Value Pairs)

var person = {
  "name": "Sam",
  "age": 40
};

Looping through a map:

person.forEach((key, value) {
  print("$key: $value");
});

🔹 13. Lambda Functions

var nums = [1, 2, 3, 4, 5];
var evens = nums.where((n) => n % 2 == 0).toList();

🔹 14. Higher-Order Functions

Functions that accept other functions.

nums.forEach((n) => print(n));

🔹 15. Sorting Lists

Ascending

nums.sort((a, b) => a.compareTo(b));

Descending

nums.sort((a, b) => b.compareTo(a));

🔹 16. Custom Sort Example (Bubble Sort)

List bubbleSort(List items) {
  for (var i = 0; i < items.length; i++) {
    for (var j = 0; j < items.length - 1; j++) {
      if (items[j] > items[j + 1]) {
        var temp = items[j];
        items[j] = items[j + 1];
        items[j + 1] = temp;
      }
    }
  }
  return items;
}

✅ Final Thoughts

This Dart cheat sheet covers:

• Core syntax
• Functional programming concepts
• Collections
• Real-world usage patterns

Perfect for:
✅ Flutter developers
✅ Interview prep
✅ Quick revision