C++

C++ is a procedural programming language for general-purpose programming.

Getting started

hello.cpp 

#include <iostream>

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

Compiling and running

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

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 -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

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 World!\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

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

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;
}

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 = "Hello world!";
for (char c: hello)
{
    std::cout << c << " ";
}
// Outputs: H e l l o w o r l d !

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;

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);
}

Classes & Objects

If statement

If statement

If statement

If statement

Preprocessor

Preprocessor

Includes 

#include "iostream"
#include <iostream>

Defines 

#define FOO
#define FOO "hello"

#undef FOO

If 

#ifdef DEBUG
  printf("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

Preprocessor

Also see