Cpp

C Programming

C++ from the basics

Statically typed language i.e. variables are checked during compile time

Preprocessor

A program that processes the source code before the compiler sees it.
First, replaces all the comments then detects everything that starts with a pound symbol. Secondly, all preprocessor directives get handled and they are replaced by the intended code. OS specific conditional compilation (click here)

namespaces

Organize and group related code into a logical scope to prevent name conflicts. Let, another company develops cout. What to do? That company should use namespace, std::cout is safe already by its namespace. Click here for example

std namespace

• Isn’t defined in one place and the while is built from multiple headers
• std namespace is like a book & each header file contributes a chapter to it. when you include a header you only get access to the relevant part of std

Expression

A sequence of operators and operands that compute a value

Statement

A valid line of code that gets executed and contains one ore many expressions

int age; // statement
age // expression
20 + 11 // expression
age < 20 // expression
age = 65 // expression
age = 65; // statement

Debugging

info registers # shows all registers’ contents
print $pc # prints program counter

Variable declaration and definition

int a = 10;
int b (10);
int c {10};

Variable scope | Local scope is checked first

#include <iostream>

int age {10};

int main() {
    int age {20};
    std::cout << age << std::endl; // 20
    return 0;
}

Type conversions

When operands are of different types, they all must come to the same type as operations only happen with the same type of operands. Coercion will be attempted and if that can’t happen, compilation error will occur.

Higher types are the types with higher capacity and lower are the opposite.
lower types typically get converted to higher ones. short, char gets converted to int automatically

auto a = 22;
double result = static_cast<double> (a) / 7; 
cout << result << endl; // 3.14286

auto b = 22;
double output = b / 7;
cout << output << endl; // 3

size_t | large enough to hold any object in cpp for a particular platform

bitwise operator

& | ^ << >>

Operator precedence & associativity

First, the operators with higher precedence will get executed
Secondly, operators at the same precedence level, will be executed according to their associativity.

int a = 19, b = 12, c = 78;
cout << a - b + c << endl; // associativity (19-12)+78 =  85

auto

Automatically detect types but types are set at runtime

auto a = 10;
a = "Utshaw"; // compilation error: invalid conversion from 'const char*' to 'int' [-fpermissive]

constants

Array

const int prices[]  {22, 22, 21, 22}; // auto size calculation

const int ages[5]  {100};
cout << ages[2] << endl; // 0

Vector | #include <vector>

Deep copy with vector:

vector<int> vec{10, 20}; // copying deeply
vector<int> new_vec {vec};
vec[0] = 88;
cout << new_vec[0] << endl; // 10
cout << vec[0] << endl; // 88

// ...
vector<int> vec{10, 20};
vector<int> new_vec = vec; // assignment does deep copy too
vec[0] = 88;
cout << new_vec[0] << endl; // 10
cout << vec[0] << endl; // 88

vector<int> prices (7, 10); // 7 elements are initialized to 10
cout << prices.size() << endl; // 7
cout << prices.at(3) << endl; // 10

vector<int> temperatures {23, 24}; // 2 elements, initialized as mentioned
cout << temperatures.size() << endl; // 2

vector<double> gpas (8, 4.00); // 8 elements, all are 4.00
cout << gpas[7] << endl; // 4

vector<vector<int>> prices {
    {10, 22, 8},
    {30, 30, 31},
    {40, 42, 41},
}; 
cout << prices.at(2).at(1) << endl; // 42

cstring | all functions treat a sequence as a string up to \0 or null

char name[] {"Farhan\0Tanvir"};
cout << strlen(name) << endl; // 6
char full_name[50] {0}; // initialize the whole array with null
strcpy(full_name, "Farhan Tanvir");
cout << strlen(full_name) << endl; // 13

Time complexity for strlen(str) is O(n)

string

string name;
getline(cin, name);
cout << name << endl;

cout << name.substr(7,6) << endl; // substr(start_index, length_in_total) Tanvir
cout << name.find("Tan") << endl; // index of "Tan" 7
cout << (name.find("Utshaw") == string::npos) << endl; // 1
name.erase(7, 6); // (start_index, length) erase length amount from start_index
cout << name.length() << endl; // 7 O(1) time complexity

string battery (3, 'A');
cout << battery << endl; //AAA
cout << battery.length() << endl; // 3