C++ Cheat Sheet: Your Quick Guide to Syntax and Concepts (with Examples)

Are you learning C++ or need a quick refresher? This C++ cheat sheet covers essential concepts, syntax, and examples to help you write efficient and effective code. This guide is great for beginners and experienced coders alike.

C++ Cheatsheet

C++ is a powerful, high-level programming language used for everything from system software to game development. Let's dive into the fundamentals!

Your First C++ Program: "Hello, World!"

Let's start with a classic example to illustrate the basic structure:

#include <iostream>
using namespace std;

int main() {
  cout << "Hello World!";
  return 0;
}

Output:

Hello World!

Understanding the Basic C++ Syntax

Every C++ program follows a specific structure:

// Header files (Include libraries)
#include <iostream>

// Use standard namespace
using namespace std;

// Main function - execution starts here
int main() {
  // Your code statements go here
  return 0; // Indicates successful execution
}

#include <iostream>: Includes the iostream library for input/output operations.
using namespace std;: Avoids repeatedly typing std:: before elements like cout and cin.
int main() { ... }: The main function where the program execution begins.
return 0;: Indicates that the program executed successfully.

Mastering Comments in C++

Comments are essential for code readability and explaining your logic.

Single-Line Comments: Use // to comment out a single line.
```
// This is a comment
cout << "GeeksforGeeks";
```

Multi-Line Comments: Use /* ... */ to comment out multiple lines.

/* This is a
   multi-line comment. */
cout << "GeeksforGeeks";

Comments are your friends. Use them to explain what you are doing.

Declaring Variables: The Foundation of Storage

Variables are named storage locations for holding data.

Must be declared before use.
Can store values of a specific data type.
Variable names can include letters, digits, and underscores, but must start with a letter or underscore.

Variable Declaration Syntax

// Declaring a single variable
data_type var_name;

// Declaring multiple variables
data_type var1_name, var2_name, var3_name;

Essential Data Types in C++

Data types define the kind of values a variable can hold.

Integer (int): Stores whole numbers (e.g., int var = 123;). Takes 4 bytes of memory.
Character (char): Stores single characters (e.g., char var = 'a';). Takes 1 byte of memory.
Floating Point (float): Stores single-precision decimal numbers (e.g., float num = 1.23;). Takes 4 bytes of memory.
Double (double): Stores double-precision decimal numbers (e.g., double num = 1.2345;). Takes 8 bytes of memory.
Boolean (bool): Stores true or false values (e.g., bool b = false;).
String (string): Stores sequences of characters (text). Requires the <string> header.
```
#include <string>
string str = "GeeksforGeeks";
```

Input and Output Operations in C++

Input (cin): Reads data from the user.
```
int var;
cin >> var;
```
Output (cout): Prints data to the console.
```
cout << "Hello World";
```

New Lines: Use \n or endl to insert line breaks.

cout << "Hello World!\n";
cout << "Hello World!" << endl;

Conditional Statements: Making Decisions

Conditional statements control the flow of execution based on conditions.

if Statement: Executes a block of code if a condition is true.

if (condition) {
  // Code to execute if condition is true
}

Nested if Statement: An if statement inside another if statement.

if (condition1) {
  // Code to execute if condition1 is true
  if (condition2) {
    // Code to execute if both condition1 and condition2 are true
  }
}

if-else Statement: Executes one block of code if a condition is true and another if it's false.

if (condition) {
  // Code to execute if condition is true
} else {
  // Code to execute if condition is false
}

else if Statement: Checks multiple conditions sequentially.

if (condition1) {
  // Code to execute if condition1 is true
} else if (condition2) {
  // Code to execute if condition1 is false and condition2 is true
} else {
  // Code to execute if all conditions are false
}

Ternary Operator: A shorthand for if-else statements.
```
(condition) ? expression1 : expression2;
```

switch Statement: Executes different code blocks based on the value of an expression.

switch (expression) {
  case value1:
    // Code to execute if expression matches value1
    break;
  case value2:
    // Code to execute if expression matches value2
    break;
  default:
    // Code to execute if expression doesn't match any case
    break;
}

break: Exits the switch statement.
default: Executed when no case matches.

Loops: Repeating Code Blocks

Loops allow you to execute a block of code multiple times.

for Loop: Executes a block of code a fixed number of times.

for (initialization; test; update) {
  // Code to be executed repeatedly
}

while Loop: Executes a block of code repeatedly as long as a condition is true.

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

do-while Loop: Similar to while, but executes the code block at least once.
```
do {
  // Code to be executed repeatedly
} while (condition);
```

Arrays: Storing Collections of Data

Arrays store a fixed-size collection of elements of the same data type.

Declaration Syntax:

dataType array_name[size];

Example:

#include <iostream>
#include <string>
using namespace std;

int main() {
  string fruits[] = {"Apple", "Banana", "Orange", "Grapes"};

  for (int i = 0; i < 4; i++) {
    cout << "Fruit at index " << i << ": " << fruits[i] << endl;
  }

  return 0;
}

Multi-Dimensional Arrays

Arrays can have multiple dimensions (e.g., 2D arrays for tables).

Declaration Syntax:

data_type array_name[size1][size2]....[sizeN];

Working with Vectors: Dynamic Arrays

Vectors are dynamic arrays that can grow or shrink in size.

Requires the <vector> header.

Vector Declaration Syntax

#include <vector>
vector<data_type> vector_name;

Common Functions

push_back(): Adds an element to the end.
pop_back(): Removes the last element.
clear(): Removes all elements.
empty(): Checks if the vector is empty.
at(i): Accesses the element at index i.
front(): Accesses the first element.
back(): Accesses the last element.
erase(): Removes an element at a specific position.

#include <iostream>
#include <vector>
using namespace std;

int main() {
  vector<int> numbers;

  numbers.push_back(10);
  numbers.push_back(20);
  numbers.push_back(30);

  cout << "Element at index 0: " << numbers.at(0) << endl; // Output: 10

  return 0;
}

References and Pointers: Working with Memory Addresses

References

A reference is an alias for an existing variable.

Declared using the & operator.

int var = 12;
int& ref = var; // ref is a reference to var

Pointers

A pointer stores the memory address of another variable.

Declared using the * operator.

Use the & operator to get the address of a variable.

int i = 3;
int *ptr = &i; // ptr stores the address of i

Functions: Reusable Code Blocks

Functions are blocks of code that perform specific tasks.

Function Declaration (Prototype): Specifies the function's name, return type, and parameters.
```
return_type function_name(parameters);
```

Function Definition: Contains the actual code that the function executes.

return_type function_name(parameters) {
  // Function body
  return value; // If the function returns a value
}

#include <iostream>
using namespace std;

int sum(int a, int b); // Function declaration

int sum(int a, int b) { // Function definition
  return a + b;
}

int main() {
  int result = sum(3, 4); // Function call
  cout << "Sum: " << result << endl; // Output: Sum: 7
  return 0;
}

String Manipulation Functions

C++ provides several functions for working with strings.

length() Function: Returns the length of a string.

#include <iostream>
#include <string>
using namespace std;

int main() {
  string str = "GeeksforGeeks";
  cout << "The length of the string is: " << str.length() << endl;
  return 0;
}

substr() Function: Extracts a substring from a string.

#include <iostream>
#include <string>
using namespace std;

int main() {
  string str = "GeeksforGeeks";
  string sub = str.substr(1, 5);
  cout << "Substring: " << sub << endl; // Output: eeksf
  return 0;
}

append() Function: Appends one string to the end of another.

#include <iostream>
#include <string>
using namespace std;

int main() {
  string str = "Geeksfor";
  str.append("Geeks");
  cout << "Appended string: " << str << endl; // Output: GeeksforGeeks
  return 0;
}

compare() Function: Compares two strings.

#include <iostream>
#include <string>
using namespace std;

int main() {
  string str1 = "Geeks";
  string str2 = "for";
  string str3 = "Geeks";

  int result1 = str1.compare(str2);
  cout << "Comparison result: " << result1 << endl; // Output: A negative value

  return 0;
}

empty() Function: Checks if a string is empty.

#include <iostream>
#include <string>
using namespace std;

int main() {
  string str1 = "GeeksforGeeks";
  string str2 = "";

  if (str1.empty()) {
    cout << "str1 is empty" << endl;
  } else {
    cout << "str1 is not empty" << endl; // Output: str1 is not empty
  }

  if (str2.empty()) {
    cout << "str2 is empty" << endl;   // Output: str2 is empty
  } else {
    cout << "str2 is not empty" << endl;
  }

  return 0;
}

Object-Oriented Programming (OOP) Concepts

C++ supports OOP principles.

1. Classes and Objects

A class is a blueprint for creating objects. An object is an instance of a class.

2. Encapsulation

Bundling data (attributes) and methods (functions) that operate on the data within a class.

3. Polymorphism

The ability of an object to take on many forms.

Types of Polymorphism

Compile-time Polymorphism
Runtime Polymorphism

4. Inheritance

A mechanism where a new class (derived class) inherits properties and behaviors from an existing class (base class), promoting code reuse and establishing hierarchical relationships between classes.

C++ Cheat Sheet: Your Quick Guide to Syntax and Concepts (with Examples)

C++ Cheatsheet

C++ is a powerful, high-level programming language used for everything from system software to game development. Let's dive into the fundamentals!

Your First C++ Program: "Hello, World!"

Let's start with a classic example to illustrate the basic structure:

#include <iostream>
using namespace std;

int main() {
  cout << "Hello World!";
  return 0;
}

Output:

Hello World!

Understanding the Basic C++ Syntax

Every C++ program follows a specific structure:

// Header files (Include libraries)
#include <iostream>

// Use standard namespace
using namespace std;

// Main function - execution starts here
int main() {
  // Your code statements go here
  return 0; // Indicates successful execution
}

#include <iostream>: Includes the iostream library for input/output operations.
using namespace std;: Avoids repeatedly typing std:: before elements like cout and cin.
int main() { ... }: The main function where the program execution begins.
return 0;: Indicates that the program executed successfully.

Mastering Comments in C++

Comments are essential for code readability and explaining your logic.

Single-Line Comments: Use // to comment out a single line.
```
// This is a comment
cout << "GeeksforGeeks";
```

Multi-Line Comments: Use /* ... */ to comment out multiple lines.

/* This is a
   multi-line comment. */
cout << "GeeksforGeeks";

Comments are your friends. Use them to explain what you are doing.

Declaring Variables: The Foundation of Storage

Variables are named storage locations for holding data.

Must be declared before use.
Can store values of a specific data type.
Variable names can include letters, digits, and underscores, but must start with a letter or underscore.

Variable Declaration Syntax

// Declaring a single variable
data_type var_name;

// Declaring multiple variables
data_type var1_name, var2_name, var3_name;

Essential Data Types in C++

Data types define the kind of values a variable can hold.

Integer (int): Stores whole numbers (e.g., int var = 123;). Takes 4 bytes of memory.
Character (char): Stores single characters (e.g., char var = 'a';). Takes 1 byte of memory.
Floating Point (float): Stores single-precision decimal numbers (e.g., float num = 1.23;). Takes 4 bytes of memory.
Double (double): Stores double-precision decimal numbers (e.g., double num = 1.2345;). Takes 8 bytes of memory.
Boolean (bool): Stores true or false values (e.g., bool b = false;).
String (string): Stores sequences of characters (text). Requires the <string> header.
```
#include <string>
string str = "GeeksforGeeks";
```

Input and Output Operations in C++

Input (cin): Reads data from the user.
```
int var;
cin >> var;
```
Output (cout): Prints data to the console.
```
cout << "Hello World";
```

New Lines: Use \n or endl to insert line breaks.

cout << "Hello World!\n";
cout << "Hello World!" << endl;

Conditional Statements: Making Decisions

Conditional statements control the flow of execution based on conditions.

if Statement: Executes a block of code if a condition is true.

if (condition) {
  // Code to execute if condition is true
}

Nested if Statement: An if statement inside another if statement.

if (condition1) {
  // Code to execute if condition1 is true
  if (condition2) {
    // Code to execute if both condition1 and condition2 are true
  }
}

if-else Statement: Executes one block of code if a condition is true and another if it's false.

if (condition) {
  // Code to execute if condition is true
} else {
  // Code to execute if condition is false
}

else if Statement: Checks multiple conditions sequentially.

if (condition1) {
  // Code to execute if condition1 is true
} else if (condition2) {
  // Code to execute if condition1 is false and condition2 is true
} else {
  // Code to execute if all conditions are false
}

Ternary Operator: A shorthand for if-else statements.
```
(condition) ? expression1 : expression2;
```

switch Statement: Executes different code blocks based on the value of an expression.

switch (expression) {
  case value1:
    // Code to execute if expression matches value1
    break;
  case value2:
    // Code to execute if expression matches value2
    break;
  default:
    // Code to execute if expression doesn't match any case
    break;
}

break: Exits the switch statement.
default: Executed when no case matches.

Loops: Repeating Code Blocks

Loops allow you to execute a block of code multiple times.

for Loop: Executes a block of code a fixed number of times.

for (initialization; test; update) {
  // Code to be executed repeatedly
}

while Loop: Executes a block of code repeatedly as long as a condition is true.

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

do-while Loop: Similar to while, but executes the code block at least once.
```
do {
  // Code to be executed repeatedly
} while (condition);
```

Arrays: Storing Collections of Data

Arrays store a fixed-size collection of elements of the same data type.

Declaration Syntax:

dataType array_name[size];

Example:

#include <iostream>
#include <string>
using namespace std;

int main() {
  string fruits[] = {"Apple", "Banana", "Orange", "Grapes"};

  for (int i = 0; i < 4; i++) {
    cout << "Fruit at index " << i << ": " << fruits[i] << endl;
  }

  return 0;
}

Multi-Dimensional Arrays

Arrays can have multiple dimensions (e.g., 2D arrays for tables).

Declaration Syntax:

data_type array_name[size1][size2]....[sizeN];

Working with Vectors: Dynamic Arrays

Vectors are dynamic arrays that can grow or shrink in size.

Requires the <vector> header.

Vector Declaration Syntax

#include <vector>
vector<data_type> vector_name;

Common Functions

push_back(): Adds an element to the end.
pop_back(): Removes the last element.
clear(): Removes all elements.
empty(): Checks if the vector is empty.
at(i): Accesses the element at index i.
front(): Accesses the first element.
back(): Accesses the last element.
erase(): Removes an element at a specific position.

#include <iostream>
#include <vector>
using namespace std;

int main() {
  vector<int> numbers;

  numbers.push_back(10);
  numbers.push_back(20);
  numbers.push_back(30);

  cout << "Element at index 0: " << numbers.at(0) << endl; // Output: 10

  return 0;
}

References and Pointers: Working with Memory Addresses

References

A reference is an alias for an existing variable.

Declared using the & operator.

int var = 12;
int& ref = var; // ref is a reference to var

Pointers

A pointer stores the memory address of another variable.

Declared using the * operator.

Use the & operator to get the address of a variable.

int i = 3;
int *ptr = &i; // ptr stores the address of i

Functions: Reusable Code Blocks

Functions are blocks of code that perform specific tasks.

Function Declaration (Prototype): Specifies the function's name, return type, and parameters.
```
return_type function_name(parameters);
```

Function Definition: Contains the actual code that the function executes.

return_type function_name(parameters) {
  // Function body
  return value; // If the function returns a value
}

#include <iostream>
using namespace std;

int sum(int a, int b); // Function declaration

int sum(int a, int b) { // Function definition
  return a + b;
}

int main() {
  int result = sum(3, 4); // Function call
  cout << "Sum: " << result << endl; // Output: Sum: 7
  return 0;
}

String Manipulation Functions

C++ provides several functions for working with strings.

length() Function: Returns the length of a string.

#include <iostream>
#include <string>
using namespace std;

int main() {
  string str = "GeeksforGeeks";
  cout << "The length of the string is: " << str.length() << endl;
  return 0;
}

substr() Function: Extracts a substring from a string.

#include <iostream>
#include <string>
using namespace std;

int main() {
  string str = "GeeksforGeeks";
  string sub = str.substr(1, 5);
  cout << "Substring: " << sub << endl; // Output: eeksf
  return 0;
}

append() Function: Appends one string to the end of another.

#include <iostream>
#include <string>
using namespace std;

int main() {
  string str = "Geeksfor";
  str.append("Geeks");
  cout << "Appended string: " << str << endl; // Output: GeeksforGeeks
  return 0;
}

compare() Function: Compares two strings.

#include <iostream>
#include <string>
using namespace std;

int main() {
  string str1 = "Geeks";
  string str2 = "for";
  string str3 = "Geeks";

  int result1 = str1.compare(str2);
  cout << "Comparison result: " << result1 << endl; // Output: A negative value

  return 0;
}

empty() Function: Checks if a string is empty.

#include <iostream>
#include <string>
using namespace std;

int main() {
  string str1 = "GeeksforGeeks";
  string str2 = "";

  if (str1.empty()) {
    cout << "str1 is empty" << endl;
  } else {
    cout << "str1 is not empty" << endl; // Output: str1 is not empty
  }

  if (str2.empty()) {
    cout << "str2 is empty" << endl;   // Output: str2 is empty
  } else {
    cout << "str2 is not empty" << endl;
  }

  return 0;
}

Object-Oriented Programming (OOP) Concepts

C++ supports OOP principles.

1. Classes and Objects

A class is a blueprint for creating objects. An object is an instance of a class.

2. Encapsulation

Bundling data (attributes) and methods (functions) that operate on the data within a class.

3. Polymorphism

The ability of an object to take on many forms.

Types of Polymorphism

Compile-time Polymorphism
Runtime Polymorphism

4. Inheritance

A mechanism where a new class (derived class) inherits properties and behaviors from an existing class (base class), promoting code reuse and establishing hierarchical relationships between classes.