cpp.md

title	C++
date	2021-06-01 04:51:44 -0700
icon	icon-cpp
background	bg-blue-800
tags
categories	Programming
intro	C++ quick reference cheat sheet that provides basic syntax and methods.

Getting started {.cols-3}

hello.cpp

#include<iostream>intmain() {
std::cout << "Hello QuickRef\n";
return0;
}

Compiling and running

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

Variables

int number = 5; // Integerfloat f = 0.95; // Floating numberdoublePI = 3.14159; // Floating numberchar yes = 'Y'; // Character
std::string s = "ME"; // String (text)bool isRight = true; // Boolean// ConstantsconstfloatRATE = 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, 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>voidhello(); // Declaringintmain() { // main functionhello(); // Calling
}
voidhello() { // 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>namespacens1 {intval(){return5;}}
intmain()
{
std::cout << ns1::val();
}

---

#include<iostream>namespacens1 {intval(){return5;}}
usingnamespacens1;usingnamespacestd;intmain()
{
cout << val(); }

Namespaces allow global identifiers under a name

C++ Arrays {.cols-3}

Declaration

int marks[3]; // Declaration
marks[0] = 92;
marks[1] = 97;
marks[2] = 98;
// Declare and initializeint marks[3] = {92, 97, 98};
int marks[] = {92, 97, 98};
// With empty membersint marks[3] = {92, 97};
std::cout << marks[2]; // Outputs: 0

Manipulation

┌─────┬─────┬─────┬─────┬─────┬─────┐
| 92 | 97 | 98 | 99 | 98 | 94 |
└─────┴─────┴─────┴─────┴─────┴─────┘
012345

---

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 loopfor (constint &n : ref) {
std::cout << std::string(1, n);
}
// Traditional for loopfor (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 {.cols-3}

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";
}
elseif (score >= 90) {
std::cout << "Excellent";
}
elseif (score >= 80) {
std::cout << "Very Good";
}
elseif (score >= 70) {
std::cout << "Good";
}
elseif (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
!exp	exp is false (NOT)

Bitwise Operators

Operator	Description
a & b	Binary AND
`a	b`
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) {
case0:
std::cout << "Zero";
break;
case1:
std::cout << "One";
break;
case2:
std::cout << "Two";
break;
case3:
std::cout << "Three";
break;
default:
std::cout << "What?";
break;
}

C++ Loops {.cols-3}

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>voidprint(int num)
{
std::cout << num << std::endl;
}
intmain()
{
int arr[4] = {1, 2, 3, 4 };
std::for_each(arr, arr + 4, print);
return0;
}

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 {.cols-3}

Arguments & Returns

#include<iostream>intadd(int a, int b) {
return a + b; }
intmain() {
std::cout << add(10, 20); }

add is a function taking 2 ints and returning int

Overloading

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

Built-in Functions

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

C++ Classes & Objects {.cols-3}

If statement

If statement

If statement

If statement

C++ Preprocessor {.cols-3}

Preprocessor {.row-span-3}

• if
• elif
• else
• endif
• ifdef
• ifndef
• define
• undef
• include
• line
• error
• pragma
• defined
• __has_include
• __has_cpp_attribute
• export
• import
• module {.style-none .cols-2}

Includes

#include"iostream"
#include<iostream>

Defines

#defineFOO
#defineFOO"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

#defineDEG(x) ((x) * 57.29)

Token concat

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

Stringification

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

file and line

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

Miscellaneous {.cols-3}

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}

• alignas
• alignof
• and
• and_eq
• asm
• atomic_cancel
• atomic_commit
• atomic_noexcept
• auto
• bitand
• bitor
• bool
• break
• case
• catch
• char
• char8_t
• char16_t
• char32_t
• class
• compl
• concept
• const
• consteval
• constexpr
• constinit
• const_cast
• continue
• co_await
• co_return
• co_yield
• decltype
• default
• delete
• do
• double
• dynamic_cast
• else
• enum
• explicit
• export
• extern
• false
• float
• for
• friend
• goto
• if
• inline
• int
• long
• mutable
• namespace
• new
• noexcept
• not
• not_eq
• nullptr
• operator
• or
• or_eq
• private
• protected
• public
• reflexpr
• register
• reinterpret_cast
• requires
• return
• short
• signed
• sizeof
• static
• static_assert
• static_cast
• struct
• switch
• synchronized
• template
• this
• thread_local
• throw
• true
• try
• typedef
• typeid
• typename
• union
• unsigned
• using
• virtual
• void
• volatile
• wchar_t
• while
• xor
• xor_eq
• final
• override
• transaction_safe
• transaction_safe_dynamic {.style-none .cols-5}

Preprocessor

• if
• elif
• else
• endif
• ifdef
• ifndef
• define
• undef
• include
• line
• error
• pragma
• defined
• __has_include
• __has_cpp_attribute
• export
• import
• module {.style-none .cols-2}

Also see

• C++ Infographics & Cheat Sheets(hackingcpp.com)
• C++ reference(cppreference.com)
• C++ Language Tutorials(cplusplus.com)