C++ Cheatsheet

What is C++ Programming Language?

C++ is a general-purpose programming language created by Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significantly over time, and modern C++ now has object-oriented, generic, and functional features in addition to facilities for low-level memory manipulation. It is almost always implemented as a compiled language, and many vendors provide C++ compilers, including the Free Software Foundation, LLVM, Microsoft, Intel, Oracle, and IBM, so it is available on many platforms.

Basics

Basic syntax and functions from the C++ programming language.

Boilerplate

#include <iostream>
    using namespace std;
    
    int main() {
    cout << "Welcome to C++";
    return 0;
    }

cout <<

It prints output on the screen

cout << "This is C++ Programming";

cin >>

It takes input from the user

cin >> variable_name

Data types

The data type is the type of data

Character type

Typically a single octet(one byte). It is an integer type

char variable_name;

Integer type

The most natural size of integer for the machine

int variable_name;

Float type

A single-precision floating-point value

float variable_name;

Double type

A double-precision floating-point value

double variable_name;

Void type

Represents the absence of the type

void

Boolean type

bool

 

Escape Sequences

It is a sequence of characters starting with a backslash, and it doesn't represent itself when used inside string literal.

Alarm or Beep

It produces a beep sound

\a

Backspace

It adds a backspace

\b

Form feed

\f

Newline

Newline Character

\n

Carriage return

\r

Tab

It gives a tab space

\t

Backslash

It adds a backslash

\\

Single quote

It adds a single quotation mark

\'

Question mark

It adds a question mark

\?

Octal No.

It represents the value of an octal number

\nnn

Hexadecimal No.

It represents the value of a hexadecimal number

\xhh

Null

The null character is usually used to terminate a string

\0

Comments

A comment is a code that is not executed by the compiler, and the programmer uses it to keep track of the code.

Single line comment

// It's a single line comment

Multi-line comment

/* It's a 
    multi-line
    comment
    */

Strings

It is a collection of characters surrounded by double quotes

Declaring String

// Include the string library
    #include <string>
    
    // String variable
    string variable1 = "Hello World";

append function

It is used to concatenate two strings

string firstName = "Soumodip ";
    string lastName = "Paul";
    string fullName = firstName.append(lastName);
    cout << fullName;

length function

It returns the length of the string

string variable1 = "Coding";
    cout << "The length of the string is: " << variable1.length();
    

Accessing and changing string characters

string variable1 = "Hello World";
    variable1[1] = 'i';
    cout << variable1;

 

 

Maths

C++ provides some built-in math functions that help the programmer to perform mathematical operations efficiently.

max function

It returns the larger value among the two

cout << max(25, 140);

min function

It returns the smaller value among the two

cout << min(55, 50);

sqrt function

It returns the square root of a supplied number

#include <cmath>
    
    cout << sqrt(144);

ceil function

It returns the value of x rounded up to its nearest integer

ceil(x)

floor function

It returns the value of x rounded down to its nearest integer

floor(x)

pow function

It returns the value of x to the power of y

pow(x, y)

Decision Making Instructions

Conditional statements are used to perform operations based on some condition.

If Statement

if (condition) {
    // This block of code will get executed, if the condition is True
    }

If-else Statement

if (condition) {
    // If condition is True then this block will get executed
    } else {
    // If condition is False then this block will get executed
    }

if else-if Statement

if (condition) {
    // Statements;
    }
    else if (condition){
    // Statements;
    }
    else{
    // Statements
    }

Ternary Operator

It is shorthand of an if-else statement.

variable = (condition) ? expressionTrue : expressionFalse;

Switch Case Statement

It allows a variable to be tested for equality against a list of values (cases).

switch (expression) 
    {
    case constant-expression: 
    statement1;
    statement2;
    break;
    case constant-expression: 
    statement;
    break;
    ...
    default: 
    statement;
    }

 

 

Iterative Statements

Iterative statements facilitate programmers to execute any block of code lines repeatedly and can be controlled as per conditions added by the programmer.

while Loop

It iterates the block of code as long as a specified condition is True

while (/* condition */)
    {
    /* code block to be executed */
    }

do-while loop

It is an exit controlled loop. It is very similar to the while loop with one difference, i.e., the body of the do-while loop is executed at least once even if the condition is False

do
    {
    /* code */
    } while (/* condition */);

for loop

It is used to iterate the statements or a part of the program several times. It is frequently used to traverse the data structures like the array and linked list.

for (int i = 0; i < count; i++)
    {
    /* code */
    }

Break Statement

break keyword inside the loop is used to terminate the loop

break;

Continue Statement

continue keyword skips the rest of the current iteration of the loop and returns to the starting point of the loop

continue;

References

Reference is an alias for an already existing variable. Once it is initialized to a variable, it cannot be changed to refer to another variable. So, it's a const pointer.

Creating References

string var1 = "Value1"; // var1 variable
    string &var2 = var1; // reference to var1

Pointers

Pointer is a variable that holds the memory address of another variable

Declaration

datatype *var_name; 
    
    var_name = &variable2;

Functions & Recursion

Functions are used to divide an extensive program into smaller pieces. It can be called multiple times to provide reusability and modularity to the C program.

Function Definition

return_type function_name(data_type parameter...){ 
    //code to be executed 
    }

Function Call

function_name(arguments);

Recursion

Recursion is when a function calls a copy of itself to work on a minor problem. And the function that calls itself is known as the Recursive function.

void recurse()
    {
    ... .. ...
    recurse();
    ... .. ...
    }

Object-Oriented Programming

It is a programming approach that primarily focuses on using objects and classes. The objects can be any real-world entities.

class

class Class_name {
    public: // Access specifier
    // fields
    // functions
    // blocks
    };

object

Class_name ObjectName;

Constructors

It is a special method that is called automatically as soon as the object is created.

class className { // The class
    public: // Access specifier
    className() { // Constructor
    cout << "Hello World";
    }
    };
    
    int main() {
    className obj_name; 
    return 0;
    }

Encapsulation

Data encapsulation is a mechanism of bundling the data, and the functions that use them and data abstraction is a mechanism of exposing only the interfaces and hiding the implementation details from the user.

#include<iostream> 
    using namespace std; 
    class ExampleEncap{ 
    private: 
    /* Since we have marked these data members private, 
    * any entity outside this class cannot access these 
    * data members directly, they have to use getter and 
    * setter functions. 
    */ 
    int num; 
    char ch; 
    public: 
    /* Getter functions to get the value of data members. 
    * Since these functions are public, they can be accessed 
    * outside the class, thus provide the access to data members 
    * through them 
    */ 
    int getNum() const { 
    return num; 
    } 
    char getCh() const { 
    return ch; 
    } 
    /* Setter functions, they are called for assigning the values 
    * to the private data members. 
    */ 
    void setNum(int num) { 
    this->num = num; 
    } 
    void setCh(char ch) { 
    this->ch = ch; 
    } 
    }; 
    int main(){ 
    ExampleEncap obj; 
    obj.setNum(100); 
    obj.setCh('A'); 
    cout<<obj.getNum()<<endl; 
    cout<<obj.getCh()<<endl; 
    return 0; 
    }

 

 

File Handling

File handling refers to reading or writing data from files. C provides some functions that allow us to manipulate data in the files.

Creating and writing to a text file

#include <iostream>
    #include <fstream>
    using namespace std;
    
    int main() {
    // Create and open a text file
    ofstream MyFile("filename.txt");
    
    // Write to the file
    MyFile << "File Handling in C++";
    
    // Close the file
    MyFile.close();
    }

Reading the file

It allows us to read the file line by line

getline()

Opening a File

It opens a file in the C++ program

void open(const char* file_name,ios::openmode mode);

OPEN MODES

in

Opens the file to read(default for ifstream)

fs.open ("test.txt", std::fstream::in)

out

Opens the file to write(default for ofstream)

fs.open ("test.txt", std::fstream::out)

binary

Opens the file in binary mode

fs.open ("test.txt", std::fstream::binary)

app

Opens the file and appends all the outputs at the end

fs.open ("test.txt", std::fstream::app)

ate

Opens the file and moves the control to the end of the file

fs.open ("test.txt", std::fstream::ate)

trunc

Removes the data in the existing file

fs.open ("test.txt", std::fstream::trunc)

nocreate

Opens the file only if it already exists

fs.open ("test.txt", std::fstream::nocreate)

noreplace

Opens the file only if it does not already exist

fs.open ("test.txt", std::fstream::noreplace)

Closing a file

It closes the file

myfile.close()

Exception Handling

An exception is an unusual condition that results in an interruption in the flow of the program.

try and catch block

A basic try-catch block in python. When the try block throws an error, the control goes to the except block

try {
    // code to try
    throw exception; // If a problem arises, then throw an exception
    }
    catch () {
    // Block of code to handle errors
    }