| title | description | created | updated |
|---|---|---|---|
C++ Programming language |
C++ Programming language cheatsheet contains useful code syntax with examples which is handy while coding. |
2020-04-30 |
2020-04-30 |
C++ is a widely used middle-level programming language which is used in developing major operating systems( Windows, Linux, Android, Ubuntu, iOS etc), Games, databases and compilers etc.
cin >> x: read value into the variable x from input streamcout << x: printf value to the output stream//: single line comments/* */: Multi line comments
#include <iostream>
using namespace std;
int main() {
cout << "Hello World!!";
return 0;
} #include <iostream>: iostream is a inbuilt header library which allows you to deal with input and output objects like cout etc.using namespace std: Specifies that the object and variable names can be used from standard library.cin: to accept input from standard input device i.e keyboard.cout: to print the output.main(): main function is the entry point of any C++ program.return 0: To end the main function
Open your terminal, Navigate to the directory where you have saved your program. Consider firstprogram.cpp is the name of your program.
sudo g++ -o firstprogram firstprogram.cpp./firstprogram
| Types | Data-type |
|---|---|
| Basic | int, char, float, double, short, short int, long int etc |
| Derived | array, pointer, string, etc |
| User Defined Data Type | structure, enum, Class, Union, Typedef |
data-type variable-name = value;int value = 10; // declaring int variable and assigning value 10 to it
char grade = 'A'; // declaring char variable and assigning value A to it- only letters (both uppercase and lowercase letters), digits and underscore(
_). - cannot contain white spaces
- First letter should be either a letter or an underscore(
_). - Variable type can't be changed
- Case sensitive
- Keywords cannot be used as variable names
data-type array-name[size]; // one-dimensional Array
data-type array-name[size][size]; // two-dimensional Arrayint a[5] = {1,2,3,4,5};
int a[2][3] = {
{1,2,3},
{4,5,6}
};It stores a sequence of character and it also functions like a vector. It contain many fuctions: begin(),end(),sort(),length() and many more
string s="abcde"; // string declaration
cout<<s[2]; // prints c
sort(s.begin(),s.end()); // sorts the given string
s.length(); // returns the length of the string
#include <string> // Include string (std namespace)
s1.size(), s2.size(); // Number of characters: 0, 5
s1 += s2 + ' ' + "world"; // Concatenation
s1 == "hello world" // Comparison, also <, >, !=, etc.
s1.substr(m, n); // Substring of size n starting at s1[m]
s1.c_str(); // Convert to const char*
s1 = to_string(12.05); // Converts number to string
getline(cin, s); // Read line ending in '\n'
string string1.append(string2); // It is used to concatenate two strings(string1 and string2 are two string names)| Literal | Example |
|---|---|
| Integer Literal- decimal | 255 |
| Integer Literal- octal | 0377 |
| Integer Literal- hexadecimal | 0xFF |
| Integer Literal- int | 30 |
| Integer Literal- unsigned int | 30u |
| Integer Literal- long | 30l |
| Integer Literal- unsigned long | 30ul |
| Float point Literal | 53.0f, 79.02 |
| Character literals | 'a', '1' |
| String literals | "OneCompiler", "Foo" |
| Boolean literals | true, false |
| Escape sequence | Description |
|---|---|
| \n | New line |
| \r | Carriage Return |
| ? | Question mark |
| \t | Horizontal tab |
| \v | Vertical tab |
| \f | Form feed |
| \ | Backslash |
| ' | Single quotation |
| " | Double quotation |
| \0 | Null character |
| \b | Back space |
| \a | Audible Bell |
| \ooo | Octal |
| \xhhh | Hexadecimal |
| Operator type | Description |
|---|---|
| Arithmetic Operator | + , - , * , / , % |
| comparision Operator | < , > , <= , >=, != , == |
| Bitwise Operator | & , | , ^ , >> , << , ~ |
| Logical Operator | && , ||, ! |
| Assignment Operator | = , += , -= , *= , /= , %=, <<=, >>=, &=, ^=, |= |
| Ternary Operator | ? : |
| sizeof operator | sizeof() |
| Scope Resolution Operator | :: (used to reference the global variable or member function that is out of scope.) |
| Category | Operator | Associativity |
|---|---|---|
| Postfix | () [] -> . ++ - - | Left to right |
| Unary | + - ! ~ ++ - - (type)* & sizeof | Right to left |
| Multiplicative | * / % | Left to right |
| Additive | + - | Left to right |
| Shift | << >> | Left to right |
| Relational | < <= > >= | Left to right |
auto double int struct
break else long switch
case enum register typedef
char extern return union
const float short unsigned
continue for signed void
default goto sizeof volatile
do if static while
try catch throw asm
operator new template this
public private protected inline
alignas namespace template boolif(conditional-expression)
{
//code
}if(conditional-expression)
{
//code
} else {
//code
}If-else using Ternary Operator
conditional-expression ? code1 : code2;if conditional-expression is true, code1 is executed. And, if condition is false, code2 is executed.
if(conditional-expression-1)
{
//code
} else if(conditional-expression-2) {
//code
} else if(conditional-expression-3) {
//code
}
....
else {
//code
}switch(conditional-expression){
case value1:
//code
break; //optional
case value2:
//code
break; //optional
...
default:
//code to be executed when all the above cases are not matched;
} for(Initialization; Condition; Increment/decrement){
//code
} while(condition){
//code
} do{
//code
} while(condition); Function is a sub-routine which contains set of statements.
// declaring a function
return_type function_name(parameters);
// defining a function
return_type function_name(parameters){
//code
}
// calling a function
function_name (parameters)Pointer is a variable which holds the memory information(address) of another variable of same data type.
datatype *pointername;
(or)
datatype* pointername;int x = 10, *ptr;
/*ptr = x; // Error because ptr is adress and x is value
*ptr = &x; // Error because x is adress and ptr is value */
ptr = &x; // valid because &x and ptr are addresses
*ptr = x; // valid because both x and *ptr values When a vairable is declared as a reference , it becomes an alternative name for an existing vairable.
datatype& reference_name;#include <iostream>
using namespace std;
int main(){
int x = 10;
cout<< x ; // Output is 10.
int& xref = x; // xref is a reference to x.
xref = 20; // value of x is modified to 20 using xref reference.
cout<< x ; // Output is 20 ;
return 0;
}Structure is a user-defined data type where it allows you to combine data of different data types.
struct structure_name {
member definition;
member definition;
...
member definition;
} [one or more structure variables];
struct structure_name variable name; //declaring structure variablesA class in C++ is the building block that leads to Object-Oriented programming. It is a user-defined data type, which holds its own data members and member functions, which can be accessed and used by creating an instance of that class. A C++ class is like a blueprint for an object.
class MyClass { // The class
public: // Access specifier
int myNum; // Attribute (int variable)
string myString; // Attribute (string variable)
};Enumeration data type is a user-defined data type in C++. enum keyword is used to declare a new enumeration types in C++.
enum name{constant1, constant2, constant3, ....... } var-list;enum month{January, February, March, April, May, June, July, August, September, October, November, December} name;Typedef is used to explicitly define new data type names by using the keyword typedef. It defines a name for an existing data type but doesn't create a new data type.
typedef data-type name;typedef unsigned int distance; // typedef of int Macro is defined by #define directive. Whenever a macro name is encountered by the compiler, it replaces the name with the definition of the macro. Macro definitions need not be terminated by a semi-colon(;).
//Can be writtern before or after
#inculde<iostream>
//but should be before the main()#define ll long long //ll is then refrenced as long long in the whole code#define: this keyword lets the compiler to understand the meaning of the keyword writtern next to it like in the example ll whenever written in code automatically expands as long long.
Genrally, used in Competetive coding and in big projects where need to write same function is repetetive
Vectors are same as dynamic arrays. They will be resized on element inseertions & deletions.
Functions associated with the vector are:
Following functions return iterator begin() end() rbegin() rend() cbegin() cend() crbegin() crend()
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> v1;
for (int i = 1; i <= 10; i++)
v1.push_back(i);
cout << "Output of begin and end: ";
for (auto i = v1.begin(); i != v1.end(); ++i)
cout << *i << " ";
return 0;
}If we want to initialize 2d vectors or even 3d vectors (i.e. arrays) then we need to embed the vectors inside the vector data structures accordingly i.e. if we want a 2d vector then vector is embedded inside a vector data structure like
vector<vector<int>> v2;//or we can for 3d vector like
vector<vector<vector<int>>> v3;Here are some useful vector functions you might need with short descriptions of each of them:
| Title | Description |
|---|---|
| size() | Returns the size of the vector (1-based indexing) |
| front() | Returns the first element of the vector |
| back() | Returns the last element of the vector(Useful when you don't know the vector size) |
| push_back() | Add element at the end of vector |
| pop_back() | Delete element from the end of vector |
| insert() | Insert any element at any position of your choice (You need to pass the position first as an iterator and then the element) |
| erase() | Remove elements from vector (You can either pass a single iterator denoting the position of the element to be erased or two iterators denoting the range in which you want all elements to be erased) |
Stacks are a type of container adaptors with LIFO(Last In First Out) type of working, where a new element is added at one end (top) and an element is removed from that end only.
The functions associated with stack are: empty() – Returns whether the stack is empty – Time Complexity : O(1) size() – Returns the size of the stack – Time Complexity : O(1) top() – Returns a reference to the top most element of the stack – Time Complexity : O(1) push(g) – Adds the element ‘g’ at the top of the stack – Time Complexity : O(1) pop() – Deletes the top most element of the stack – Time Complexity : O(1)
#include <iostream>
#include <stack>
using namespace std;
int main() {
stack<int> stack;
stack.push(21);
stack.push(22);
stack.push(24);
stack.push(25);
stack.pop();
stack.pop();
while (!stack.empty()) {
cout << ' ' << stack.top();
stack.pop();
}
}Queues are a type of container adaptors that operate in a first in first out (FIFO) type of arrangement. Elements are inserted at the back (end) and are deleted from the front
queue::empty() Returns whether the queue is empty. queue::size() Returns the size of the queue. queue::swap() Exchange the contents of two queues but the queues must be of the same type, although sizes may differ. queue::emplace() Insert a new element into the queue container, the new element is added to the end of the queue. queue::front() Returns a reference to the first element of the queue. queue::back() Returns a reference to the last element of the queue. queue::push(g) Adds the element ‘g’ at the end of the queue. queue::pop() removes the element
#include <iostream>
#include <queue>
using namespace std;
int main() {
queue<int> q;
q.push(21);
q.push(22);
q.push(24);
q.push(25);
q.pop();
q.pop();
while (!q.empty()) {
cout << ' ' << q.front();
q.pop();
}
}Heap data structure is a complete binary tree that satisfies the heap property, where any given node is
- Always greater than its child node/s and the key of the root node is the largest among all other nodes. This property is also called max heap property.
- Always smaller than the child node/s and the key of the root node is the smallest among all other nodes. This property is also called min heap property.
When a element inserted in heap wil be inserted in such position that greatest element will always be at top and will pe popped first.
#include<bits/stdc++.h>
using namespace std;
int main(){
priority_queue<int,vector<int>> maxh;
maxh.push(1);
maxh.push(2);
maxh.push(-1);
int greatest = maxh.top(); // greatest = 2
pq.pop();
int second_greatest = maxh.top(); // second_greatest = 1
return 0;
} When a element inserted in heap wil be inserted in such position that smallest element will always be at top and will pe popped first.
#include<bits/stdc++.h>
using namespace std;
int main(){
priority_queue<int,vector<int>,greater<int>> minh;
minh.push(1);
minh.push(2);
minh.push(-1);
int smallest = minh.top(); // smallest = -1
pq.pop();
int second_minimum = minh.top(); // second_minimum = 1
return 0;
} Hash Map (also, hash table) is a data structure that basically maps keys to values. A hash table uses a hash function to compute an index into an array of buckets or slots, from which the corresponding value can be found. It can be implemented
unordered_map<int,int> mp; //here first element is the key and second element is the value The first element is the key where the second element which is the value is stored and can be serached for in constant time
#include<bits/stdc++.h>
using namespace std;
int main(){
unordered_map<int,int> mp; //
mp.insert({1,2}); // key=1, value=2;
mp[-1]=1; // key=-1, value=1
return 0;
}There can be an ordered map too which stores the keys in order
#include<bits/stdc++.h>
using namespace std;
int main(){
map<int,int> order_mp; //
order_mp.insert({1,2}); // key=1, value=2;
order_mp[-1]=1; // key=-1, value=1
return 0;
}Sorting is one of the most basic functions applied to data. It means arranging the data in a particular fashion, which can be increasing or decreasing. There is a builtin function in C++ STL by the name of sort(). This function internally uses IntroSort. In more details it is implemented using hybrid of QuickSort, HeapSort and InsertionSort.
#include<iostream>
#include<algorithm>
using namespace std;
int main(){
int arr[] = {3,2,1};
int n = 3 ; // size of the array
sort(arr, arr+n); // sorting the array in ascending order
sort(arr, arr+n, greater<int>()); // sorting the array in descending order
vector<int> v;
v = {3,2,1};
sort(v.begin(), v.end()); // sorting in the vector in ascending order
sort(v.begin(), v.end(), greater<int>()); // sorting in the vector in descending order
//For sorting the vector in descending order, you could also use the reverse iterator
//i.e.:
sort(v.rbegin(),v.rend()); // This will also sort the vector in a descending order
//for sorting only a part of the vector , we can do:
//sort(v.begin()+start_index,v.begin()+ending_index);
//This will sort only part of the array from start_index to end_index
}| Name | Use |
|---|---|
| #include<stdio.h> | It is used to perform input and output operations |
| #include<string.h> | It is used to perform various string operations |
| #include<math.h> | It is used to perform mathematical operations |
| #include<iomanip.h> | It is used to access set() and setprecision() |
| #include<signal.h> | It is used to perform signal handling functions like signal() and raise() |
| #include<stdarg.h> | It is used to perform standard argument functions |
| #include<errno.h> | It is used to perform error handling operations like errno |
| #include<fstream.h> | It is used to control the data to read from a file |
| #include<time.h> | It is used to perform functions related to date() and time |
| #include<graphics.h> | It is used include and facilitate graphical operations in program |
| #include<bits/stdc++.h> | It is used to include all the standard library files, this is called a NON-STANDARD header file (it can't be compiled on a compiler other than GCC) |
| #include<limits.h> | The macros in this header stores the values of variables in various data types |
| #include<setjmp.h> | It contains function prototypes for functions that allow bypassing of the normal function call and return sequence |
| #include<assert.h> | It contains information for adding diagnostics that helps in program debugging |