C++

C++ quick reference cheat sheet that provides basic syntax and methods.

#Getting started

#hello.cpp

#include <iostream>

int main() {
    std::cout << "Hello QuickRef\n";
    return 0;
}

Compiling and running

$ g++ hello.cpp -o hello
$ ./hello
Hello QuickRef

#Variables

int number = 5;       // Integer
float f = 0.95;       // Floating number
double PI = 3.14159;  // Floating number
char yes = 'Y';       // Character
std::string s = "ME"; // String (text)
bool isRight = true;  // Boolean

// Constants
const float RATE = 0.8;

int age {25};         // Since C++11
std::cout << age;     // Print 25

#Primitive Data Types

Data Type Size Range
int 4 bytes -231 to 231-1
float 4 bytes N/A
double 8 bytes N/A
char 1 byte -128 to 127
bool 1 byte true / false
void N/A N/A
wchar_t 2 or 4 bytes 1 wide character

#User Input

int num;

std::cout << "Type a number: ";
std::cin >> num;

std::cout << "You entered " << num;

#Swap

int a = 5, b = 10, temp;
temp = a;
a = b;
b = temp;

// Outputs: a=10, b=5
std::cout << "a=" << a << ", b=" << b;

#Comments

// A single one line comment in C++

/* This is a multiple line comment
   in C++ */

#If statement

if (a == 10) {
    // do something
}

See: Conditionals

#Loops

for (int i = 0; i < 10; i++) {
    std::cout << i << "\n";
}

See: Loops

#Functions

#include <iostream>
 
void hello(); // Declaring
 
int main() {  // main function
    hello();    // Calling
}
 
void hello() { // Defining
    std::cout << "Hello QuickRef!\n";
}

See: Functions

#References

int i = 1;
int& ri = i; // ri is a reference to i

ri = 2; // i is now changed to 2
std::cout << "i=" << i;

i = 3;   // i is now changed to 3
std::cout << "ri=" << ri;

ri and i refer to the same memory location.

#Namespaces

#include <iostream>
namespace ns1 {int val(){return 5;}}
int main()
{
    std::cout << ns1::val();
}

#include <iostream>
namespace ns1 {int val(){return 5;}}
using namespace ns1;
using namespace std;
int main()
{
    cout << val(); 
}

Namespaces allow global identifiers under a name

#C++ Arrays

#Declaration

int marks[3]; // Declaration
marks[0] = 92;
marks[1] = 97;
marks[2] = 98;

// Declare and initialize
int marks[3] = {92, 97, 98};
int marks[]  = {92, 97, 98};

// With empty members
int marks[3] = {92, 97};
std::cout << marks[2]; // Outputs: 0

#Manipulation

┌─────┬─────┬─────┬─────┬─────┬─────┐
| 92  | 97  | 98  | 99  | 98  | 94  |
└─────┴─────┴─────┴─────┴─────┴─────┘
   0     1     2     3     4     5

int marks[6] = {92, 97, 98, 99, 98, 94};

// Print first element
std::cout << marks[0];

// Change 2th element to 99
marks[1] = 99;

// Take input from the user
std::cin >> marks[2];

#Displaying

char ref[5] = {'R', 'e', 'f'};

// Range based for loop
for (const int &n : ref) {
    std::cout << std::string(1, n);
}

// Traditional for loop
for (int i = 0; i < sizeof(ref); ++i) {
    std::cout << ref[i];
}

#Multidimensional

     j0   j1   j2   j3   j4   j5
   ┌────┬────┬────┬────┬────┬────┐
i0 | 1  | 2  | 3  | 4  | 5  | 6  |
   ├────┼────┼────┼────┼────┼────┤
i1 | 6  | 5  | 4  | 3  | 2  | 1  |
   └────┴────┴────┴────┴────┴────┘

int x[2][6] = {
    {1,2,3,4,5,6}, {6,5,4,3,2,1}
};
for (int i = 0; i < 2; ++i) {
    for (int j = 0; j < 6; ++j) {
        std::cout << x[i][j] << " ";
    }
}
// Outputs: 1 2 3 4 5 6 6 5 4 3 2 1 

#C++ Conditionals

#If Clause

if (a == 10) {
    // do something
}

int number = 16;

if (number % 2 == 0)
{
    std::cout << "even";
}
else
{
    std::cout << "odd";
}

// Outputs: even

#Else if Statement

int score = 99;
if (score == 100) {
    std::cout << "Superb";
}
else if (score >= 90) {
    std::cout << "Excellent";
}
else if (score >= 80) {
    std::cout << "Very Good";
}
else if (score >= 70) {
    std::cout << "Good";
}
else if (score >= 60)
    std::cout << "OK";
else
    std::cout << "What?";

#Operators

#Relational Operators

a == b a is equal to b
a != b a is NOT equal to b
a < b a is less than b
a > b a is greater b
a <= b a is less than or equal to b
a >= b a is greater or equal to b

#Assignment Operators

Example Equivalent to
a += b Aka a = a + b
a -= b Aka a = a - b
a *= b Aka a = a * b
a /= b Aka a = a / b
a %= b Aka a = a % b

#Logical Operators

Example Meaning
exp1 && exp2 Both are true (AND)
exp1 || exp2 Either is true (OR)
!exp exp is false (NOT)

#Bitwise Operators

Operator Description
a & b Binary AND
a | b Binary OR
a ^ b Binary XOR
a ~ b Binary One's Complement
a << b Binary Shift Left
a >> b Binary Shift Right

#Ternary Operator

           ┌── True ──┐
Result = Condition ? Exp1 : Exp2;
           └───── False ─────┘

int x = 3, y = 5, max;
max = (x > y) ? x : y;

// Outputs: 5
std::cout << max << std::endl;

int x = 3, y = 5, max;
if (x > y) {
    max = x;
} else {
    max = y;
}
// Outputs: 5
std::cout << max << std::endl;

#Switch Statement

int num = 2;
switch (num) {
    case 0:
        std::cout << "Zero";
        break;
    case 1:
        std::cout << "One";
        break;
    case 2:
        std::cout << "Two";
        break;
    case 3:
        std::cout << "Three";
        break;
    default:
        std::cout << "What?";
        break;
}

#C++ Loops

#While

int i = 0;
while (i < 6) {
    std::cout << i++;
}

// Outputs: 012345

#Do-while

int i = 1;
do {
    std::cout << i++;
} while (i <= 5);

// Outputs: 12345

#Continue statements

for (int i = 0; i < 10; i++) {
    if (i % 2 == 0) {
        continue;
    }
    std::cout << i;
} // Outputs: 13579

#Infinite loop

while (true) { // true or 1
    std::cout << "infinite loop";
}

for (;;) {
    std::cout << "infinite loop";
}

for(int i = 1; i > 0; i++) {
    std::cout << "infinite loop";
}

#for_each (Since C++11)

#include <iostream>

void print(int num)
{
    std::cout << num << std::endl;
}

int main()
{
    int arr[4] = {1, 2, 3, 4 };
    std::for_each(arr, arr + 4, print);
    return 0;
}

#Range-based (Since C++11)

int num_array[] = {1, 2, 3, 4, 5};
for (int n : num_array) {
    std::cout << n << " ";
}
// Outputs: 1 2 3 4 5

std::string hello = "QuickRef.ME";
for (char c: hello)
{
    std::cout << c << " ";
}
// Outputs: Q u i c k R e f . M E 

#Break statements

int password, times = 0;
while (password != 1234) {
    if (times++ >= 3) {
        std::cout << "Locked!\n";
        break;
    }
    std::cout << "Password: ";
    std::cin >> password; // input
}

#Several variations

for (int i = 0, j = 2; i < 3; i++, j--){
    std::cout << "i=" << i << ",";
    std::cout << "j=" << j << ";";
}
// Outputs: i=0,j=2;i=1,j=1;i=2,j=0;

#C++ Functions

#Arguments & Returns

#include <iostream>

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

int main() {
    std::cout << add(10, 20); 
}

add is a function taking 2 ints and returning int

#Overloading

void fun(string a, string b) {
    std::cout << a + " " + b;
}
void fun(string a) {
    std::cout << a;
}
void fun(int a) {
    std::cout << a;
}

#Built-in Functions

#include <iostream>
#include <cmath> // import library
 
int main() {
    // sqrt() is from cmath
    std::cout << sqrt(9);
}

#C++ Classes & Objects

#If statement


#If statement


#If statement


#If statement


#C++ Preprocessor

#Includes

#include "iostream"
#include <iostream>

#Defines

#define FOO
#define FOO "hello"

#undef FOO

#If

#ifdef DEBUG
  console.log('hi');
#elif defined VERBOSE
  ...
#else
  ...
#endif

#Error

#if VERSION == 2.0
  #error Unsupported
  #warning Not really supported
#endif

#Macro

#define DEG(x) ((x) * 57.29)

#Token concat

#define DST(name) name##_s name##_t
DST(object);   #=> object_s object_t;

#Stringification

#define STR(name) #name
char * a = STR(object);   #=> char * a = "object";

#file and line

#define LOG(msg) console.log(__FILE__, __LINE__, msg)
#=> console.log("file.txt", 3, "hey")

#Also see