title: C++ date: 2021-06-01 11:51:44 background: bg-[#6d94c7] tags: categories: - Programming intro: |

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

```shell script \( g++ hello.cpp -o hello \) ./hello Hello QuickRef


### Variables

```cpp
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 -2^31^ ^to^ 2^31^-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

{.show-header}

User Input

int num;

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

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

Swap

int a = 5, b = 10;
std::swap(a, b);

// 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

std::array<int, 3> marks; // Definition
marks[0] = 92;
marks[1] = 97;
marks[2] = 98;

// Define and initialize
std::array<int, 3> = {92, 97, 98};

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

Manipulation

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

std::array<int, 6> marks = {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 {.row-span-2}

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 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>

int main()
{
    auto print = [](int num) { std::cout << num << std::endl; };

    std::array<int, 4> arr = {1, 2, 3, 4};
    std::for_each(arr.begin(), arr.end(), print);
    return 0;
}

Range-based (Since C++11)

for (int n : {1, 2, 3, 4, 5}) {
    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

Preprocessor {.row-span-3}

Includes

#include "iostream"
#include <iostream>

Defines

#define FOO
#define FOO "hello"

#undef FOO

If {.row-span-2}

#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")

Miscellaneous

Escape Sequences

Escape Sequences Characters
\b Backspace
\f Form feed
\n Newline
\r Return
\t Horizontal tab
\v Vertical tab
\\ Backslash
\' Single quotation mark
\" Double quotation mark
\? Question mark
\0 Null Character

Keywords {.col-span-2 .row-span-2}

Preprocessor

Also see