Top 50 C++ Keywords & Functions

#CPP #Basics #IO

#1. #include <iostream>
A preprocessor directive that includes the input/output stream library.

#include <iostream>

int main() {
    std::cout << "This requires iostream!";
    return 0;
}

This requires iostream!

#2. int main()
The main function where program execution begins.

#include <iostream>

int main() {
    std::cout << "Program starts here.";
    return 0;
}

Program starts here.

#3. std::cout
Used to output data (print to the console).

#include <iostream>

int main() {
    std::cout << "Hello, C++!";
    return 0;
}

Hello, C++!

#4. std::cin
Used to get input from the user.

#include <iostream>
#include <string>

int main() {
    int age;
    std::cout << "Enter your age: ";
    std::cin >> age;
    std::cout << "You are " << age << " years old.";
    return 0;
}

Enter your age: 25
You are 25 years old.

#5. using namespace std;
Tells the compiler to use the std (standard) namespace. Avoids prefixing std:: to every standard function.

#include <iostream>
using namespace std;

int main() {
    cout << "No std:: prefix needed.";
    return 0;
}

No std:: prefix needed.

---
#CPP #DataTypes #Variables

#6. int
Declares an integer variable.

#include <iostream>

int main() {
    int number = 100;
    std::cout << "The number is: " << number;
    return 0;
}

The number is: 100

#7. double
Declares a floating-point number variable (can hold decimals).

#include <iostream>

int main() {
    double price = 19.99;
    std::cout << "The price is: " << price;
    return 0;
}

The price is: 19.99

#8. char
Declares a character variable.

#include <iostream>

int main() {
    char grade = 'A';
    std::cout << "Your grade is: " << grade;
    return 0;
}

Your grade is: A

#9. bool
Declares a boolean variable, which can only have the value true or false.

#include <iostream>

int main() {
    bool isRaining = false;
    std::cout << "Is it raining? " << isRaining; // Outputs 0 for false
    return 0;
}

Is it raining? 0

#10. std::string
Declares a variable that can hold a sequence of characters. Requires #include <string>.

#include <iostream>
#include <string>

int main() {
    std::string greeting = "Hello, World!";
    std::cout << greeting;
    return 0;
}

Hello, World!

---
#CPP #Keywords #Operators

#11. const
Declares a variable as a constant, meaning its value cannot be changed.

#include <iostream>

int main() {
    const double PI = 3.14159;
    std::cout << "The value of PI is: " << PI;
    // PI = 4; // This would cause a compile error
    return 0;
}

The value of PI is: 3.14159

#12. sizeof()
An operator that returns the size (in bytes) of a data type or variable.

#include <iostream>

int main() {
    int myInt;
    std::cout << "Size of int is: " << sizeof(myInt) << " bytes.";
    return 0;
}

Size of int is: 4 bytes.

#13. auto
A keyword that lets the compiler automatically deduce the data type of a variable at compile-time.

#include <iostream>

int main() {
    auto number = 10; // Compiler deduces int
    auto pi = 3.14;   // Compiler deduces double
    std::cout << "Type of 'number' is deduced.";
    return 0;
}

Type of 'number' is deduced.

#14. & (Address-of Operator)
Returns the memory address of a variable.

#include <iostream>

int main() {
    int var = 20;
    std::cout << "Memory address of var: " << &var;
    return 0;
}

Memory address of var: 0x61ff08 
(Note: Address will vary)

#15. * (Dereference Operator)
Accesses the value stored at a memory address held by a pointer.

#include <iostream>

int main() {
    int var = 50;
    int* ptr = &var; // ptr holds the address of var
    std::cout << "Value at address " << ptr << " is " << *ptr;
    return 0;
}

Value at address 0x61ff04 is 50
(Note: Address will vary)

---
#CPP #ControlFlow #Conditional

#16. if
Executes a block of code if a specified condition is true.

#include <iostream>

int main() {
    int age = 18;
    if (age >= 18) {
        std::cout << "You are an adult.";
    }
    return 0;
}

You are an adult.

#17. else
Executes a block of code if the condition in the if statement is false.

#include <iostream>

int main() {
    int age = 16;
    if (age >= 18) {
        std::cout << "You are an adult.";
    } else {
        std::cout << "You are not an adult.";
    }
    return 0;
}

You are not an adult.

#18. else if
Specifies a new condition to test, if the first if condition is false.

#include <iostream>

int main() {
    int score = 85;
    if (score >= 90) {
        std::cout << "Grade: A";
    } else if (score >= 80) {
        std::cout << "Grade: B";
    } else {
        std::cout << "Grade: C";
    }
    return 0;
}

Grade: B

#19. switch / case
Selects one of many code blocks to be executed.

#include <iostream>

int main() {
    int day = 3;
    switch (day) {
        case 1:
            std::cout << "Monday";
            break;
        case 2:
            std::cout << "Tuesday";
            break;
        case 3:
            std::cout << "Wednesday";
            break;
    }
    return 0;
}

Wednesday

#20. break
Used to exit a switch statement or a loop.

#include <iostream>

int main() {
    for (int i = 0; i < 10; ++i) {
        if (i == 5) {
            break; // Exit the loop when i is 5
        }
        std::cout << i << " ";
    }
    return 0;
}

0 1 2 3 4

---
#CPP #Loops

#21. for
Executes a block of code a specified number of times.

#include <iostream>

int main() {
    for (int i = 0; i < 5; ++i) {
        std::cout << i << " ";
    }
    return 0;
}

0 1 2 3 4

#22. while
Loops through a block of code as long as a specified condition is true.

#include <iostream>

int main() {
    int i = 0;
    while (i < 5) {
        std::cout << i << " ";
        i++;
    }
    return 0;
}

0 1 2 3 4

#23. do-while
Similar to a while loop, but the code block is executed at least once before the condition is tested.

#include <iostream>

int main() {
    int i = 5;
    do {
        std::cout << "This will run once.";
        i++;
    } while (i < 5);
    return 0;
}

This will run once.

#24. Range-based for loop
Iterates over all elements in a range, such as an array or vector, without using an index.

#include <iostream>
#include <vector>

int main() {
    int numbers[] = {10, 20, 30};
    for (int num : numbers) {
        std::cout << num << " ";
    }
    return 0;
}

10 20 30

#25. continue
Skips the current iteration of a loop and continues with the next iteration.

#include <iostream>

int main() {
    for (int i = 0; i < 5; ++i) {
        if (i == 2) {
            continue; // Skip printing 2
        }
        std::cout << i << " ";
    }
    return 0;
}

0 1 3 4

---
#CPP #Functions

#26. Function Declaration (Prototype)
Declares a function's name, return type, and parameters, allowing it to be used before it's defined.

#include <iostream>

void sayHello(); // Function declaration

int main() {
    sayHello(); // Call the function
    return 0;
}

void sayHello() { // Function definition
    std::cout << "Hello from function!";
}

Hello from function!

#27. void
A keyword specifying that a function does not return any value.

#include <iostream>

void printMessage(std::string message) {
    std::cout << message;
}

int main() {
    printMessage("This function returns nothing.");
    return 0;
}

This function returns nothing.

#28. return
Terminates a function and can return a value to the caller.

#include <iostream>

int add(int a, int b) {
    return a + b; // Return the sum
}

int main() {
    int result = add(5, 3);
    std::cout << "Result: " << result;
    return 0;
}

Result: 8

#29. #include <cmath>
Includes the C++ math library for complex mathematical operations.

#include <iostream>
#include <cmath> // Include for sqrt()

int main() {
    double number = 25.0;
    std::cout << "Square root is: " << sqrt(number);
    return 0;
}

Square root is: 5

#30. pow()
A function from <cmath> that returns the base raised to the power of the exponent.

#include <iostream>
#include <cmath>

int main() {
    double result = pow(2, 3); // 2 to the power of 3
    std::cout << "2^3 is: " << result;
    return 0;
}

2^3 is: 8

---
#CPP #STL #Vector

#31. #include <vector>
Includes the library for std::vector, a dynamic array.

#include <iostream>
#include <vector>

int main() {
    std::vector<int> myVector;
    myVector.push_back(1);
    std::cout << "Vector is ready.";
    return 0;
}

Vector is ready.

#32. std::vector
A sequence container that encapsulates dynamic size arrays.

#include <iostream>
#include <vector>

int main() {
    std::vector<int> numbers = {10, 20, 30};
    std::cout << "First element: " << numbers[0];
    return 0;
}

First element: 10

#33. .push_back()
Member function of std::vector that adds an element to the end.

#include <iostream>
#include <vector>

int main() {
    std::vector<int> numbers;
    numbers.push_back(5);
    numbers.push_back(10);
    std::cout << "Vector size: " << numbers.size();
    return 0;
}

Vector size: 2

#34. .size()
Member function that returns the number of elements in a container like std::vector or std::string.

#include <iostream>
#include <vector>

int main() {
    std::vector<std::string> fruits = {"Apple", "Banana"};
    std::cout << "There are " << fruits.size() << " fruits.";
    return 0;
}

There are 2 fruits.

#35. .length()
A member function of std::string that returns its length. It's synonymous with .size().

#include <iostream>
#include <string>

int main() {
    std::string text = "C++";
    std::cout << "The length of the string is: " << text.length();
    return 0;
}

The length of the string is: 3

---
#CPP #STL #Algorithms

#36. #include <algorithm>
Includes the standard library algorithms, like sort, find, copy, etc.

#include <iostream>
#include <vector>
#include <algorithm> // Required for std::sort

int main() {
    std::vector<int> nums = {3, 1, 4};
    std::sort(nums.begin(), nums.end());
    std::cout << "Sorting is possible with <algorithm>.";
    return 0;
}

Sorting is possible with <algorithm>.

#37. std::sort()
Sorts the elements in a range (e.g., a vector).

#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> nums = {50, 20, 40, 10, 30};
    std::sort(nums.begin(), nums.end());
    for(int n : nums) {
        std::cout << n << " ";
    }
    return 0;
}

10 20 30 40 50

#38. .begin()
Returns an iterator pointing to the first element in a container.

#include <iostream>
#include <vector>

int main() {
    std::vector<int> nums = {100, 200, 300};
    auto it = nums.begin();
    std::cout << "First element: " << *it;
    return 0;
}

First element: 100

#39. .end()
Returns an iterator referring to the past-the-end element in the container.

#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> nums = {1, 2, 3};
    // .end() points after the last element, used as a boundary
    std::cout << "Vector has elements until the end.";
    return 0;
}

Vector has elements until the end.

#40. #define
A preprocessor directive used to create macros or symbolic constants.

#include <iostream>
#define PI 3.14159

int main() {
    std::cout << "The value of PI is " << PI;
    return 0;
}

The value of PI is 3.14159

---
#CPP #OOP #Classes

#41. class
A keyword used to declare a class, which is a blueprint for creating objects.

#include <iostream>

class Dog {
public:
    void bark() {
        std::cout << "Woof!";
    }
};

int main() {
    Dog myDog;
    myDog.bark();
    return 0;
}

Woof!

#42. struct
Similar to a class, but its members are public by default.

#include <iostream>

struct Point {
    int x;
    int y;
};

int main() {
    Point p;
    p.x = 10;
    p.y = 20;
    std::cout << "Point: (" << p.x << ", " << p.y << ")";
    return 0;
}

Point: (10, 20)

#43. public
An access specifier that makes class members accessible from outside the class.

#include <iostream>

class MyClass {
public: // Accessible from anywhere
    int myNum = 10;
};

int main() {
    MyClass obj;
    std::cout << obj.myNum;
    return 0;
}

10

#44. private
An access specifier that makes class members accessible only from within the class itself.

#include <iostream>

class MyClass {
private:
    int secret = 42;
public:
    void printSecret() {
        std::cout << secret; // Accessible from within the class
    }
};

int main() {
    MyClass obj;
    // std::cout << obj.secret; // This would cause a compile error
    obj.printSecret();
    return 0;
}

42

#45. Constructor
A special member function of a class that is executed whenever a new object of that class is created.

#include <iostream>

class Car {
public:
    // Constructor
    Car() {
        std::cout << "Car object created.";
    }
};

int main() {
    Car myCar; // Constructor is called here
    return 0;
}

Car object created.

---
#CPP #OOP #MemoryManagement

#46. Destructor
A special member function that is executed automatically when an object is destroyed.

#include <iostream>

class MyClass {
public:
    // Destructor
    ~MyClass() {
        std::cout << "Object destroyed.";
    }
};

int main() {
    MyClass obj;
    // Destructor is called when main() ends
    return 0;
}

Object destroyed.

#47. this
A keyword that refers to the current instance of the class.

#include <iostream>

class Box {
private:
    int length;
public:
    Box(int length) {
        this->length = length; // Use 'this' to distinguish member from parameter
    }
    void printLength() {
        std::cout << "Length: " << this->length;
    }
};

int main() {
    Box b(10);
    b.printLength();
    return 0;
}

Length: 10

#48. new
An operator that allocates memory on the heap and returns a pointer to it.

#include <iostream>

int main() {
    int* ptr = new int; // Allocate an integer on the heap
    *ptr = 100;
    std::cout << "Value from heap: " << *ptr;
    delete ptr; // Must deallocate memory
    return 0;
}

Value from heap: 100

#49. delete
An operator that deallocates memory previously allocated with new.

#include <iostream>

int main() {
    int* ptr = new int(55);
    std::cout << *ptr << " allocated. ";
    delete ptr; // Deallocate the memory
    std::cout << "Memory freed.";
    // Accessing ptr now is undefined behavior
    return 0;
}

55 allocated. Memory freed.

#50. nullptr
Represents a null pointer literal. It indicates that a pointer does not point to any valid memory location.

#include <iostream>

int main() {
    int* ptr = nullptr;
    if (ptr == nullptr) {
        std::cout << "The pointer is null.";
    }
    return 0;
}

The pointer is null.

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By: @DataScienceQ ✨