title: C++ date: 2021-06-01 11:51:44 background: bg-[#6d94c7] tags: categories: - Programming intro: |
#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
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}
int num;
std::cout << "Type a number: ";
std::cin >> num;
std::cout << "You entered " << num;
int a = 5, b = 10;
std::swap(a, b);
// Outputs: a=10, b=5
std::cout << "a=" << a << ", b=" << b;
// A single one line comment in C++
/* This is a multiple line comment
in C++ */
if (a == 10) {
// do something
}
See: Conditionals
for (int i = 0; i < 10; i++) {
std::cout << i << "\n";
}
See: Loops
#include <iostream>
void hello(); // Declaring
int main() { // main function
hello(); // Calling
}
void hello() { // Defining
std::cout << "Hello QuickRef!\n";
}
See: Functions
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.
#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
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
┌─────┬─────┬─────┬─────┬─────┬─────┐
| 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];
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];
}
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
if (a == 10) {
// do something
}
int number = 16;
if (number % 2 == 0)
{
std::cout << "even";
}
else
{
std::cout << "odd";
}
// Outputs: even
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?";
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 |
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 |
Example | Meaning |
---|---|
exp1 && exp2 |
Both are true (AND) |
exp1 || exp2 |
Either is true (OR) |
!exp |
exp is false (NOT) |
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 |
┌── 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;
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;
}
int i = 0;
while (i < 6) {
std::cout << i++;
}
// Outputs: 012345
int i = 1;
do {
std::cout << i++;
} while (i <= 5);
// Outputs: 12345
for (int i = 0; i < 10; i++) {
if (i % 2 == 0) {
continue;
}
std::cout << i;
} // Outputs: 13579
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";
}
#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;
}
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
int password, times = 0;
while (password != 1234) {
if (times++ >= 3) {
std::cout << "Locked!\n";
break;
}
std::cout << "Password: ";
std::cin >> password; // input
}
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;
#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
void fun(string a, string b) {
std::cout << a + " " + b;
}
void fun(string a) {
std::cout << a;
}
void fun(int a) {
std::cout << a;
}
#include <iostream>
#include <cmath> // import library
int main() {
// sqrt() is from cmath
std::cout << sqrt(9);
}
#include "iostream"
#include <iostream>
#define FOO
#define FOO "hello"
#undef FOO
#ifdef DEBUG
console.log('hi');
#elif defined VERBOSE
...
#else
...
#endif
#if VERSION == 2.0
#error Unsupported
#warning Not really supported
#endif
#define DEG(x) ((x) * 57.29)
#define DST(name) name##_s name##_t
DST(object); #=> object_s object_t;
#define STR(name) #name
char * a = STR(object); #=> char * a = "object";
#define LOG(msg) console.log(__FILE__, __LINE__, msg)
#=> console.log("file.txt", 3, "hey")
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 |
C++ Infographics & Cheat Sheets (hackingcpp.com)
C++ reference (cppreference.com)
C++ Language Tutorials (cplusplus.com)