Notes & Articles

This page is an introduction to the C++ language. Reading this page, you can learn some basic knowledge of C++, which can be used in this programming language to solve some basic problems.

A simple C++ programme

#include <iostream>

using namespace std;

int main() {
  cout << "Hello World" << endl;

  return 0;
}

// the programme will print text "Hello World" to the console.

Syntax

#include <iostream> is a header file library that lets us work with input and output objects, such as cout (used in line 5). Header files add functionality to C++ programs.

Variables

There are seven inner variables in the C++ language.

type keyword
Integer int
Boolean bool
Float float
Double float double
Empty void
Width Char wchar_t
  • The type of wchar_t comes from typedef short int wchar_t. As a result, ‘wchar_t’ has the same space as’short int’.

Variables can use type modifiers for modification.

Data Types

type size
boolean 1 byte
char 1 byte
int 2 or 4 bytes
float 4 bytes
double 8 bytes

User Input

cin is a predefined variable that reads data from the keyboard with the extraction operator >>.

Operators

Arithmetic Operators

Operator Name
+ Add
- Subtraction
* Multiplication
/ Division
% Modulus
++ Increment
– Decrement

Assignment Operators

Operator
=
+=
-=
*=
/=
%=
&=
|=
^=
>>=
<<=

Comparison Operators

Operator Name
== Equal to
!= Not equal
> Greater than
< Less than
>= Greater than or equal to
<= Less than or equal to

Logical Operators

Operator Name
& Logical and
| Logical or
! Logical not

Strings

A string variable contains a collection of characters surrounded by double quotes

Omitting Namespace

  • The using namespace std line can be omitted and replaced with the std keyword, followed by the :: operator for string (and cout) objects:
#include <iostream>

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


#include <iostream>
#include <string>

using namespace std;

namespace test
{
  string testStr = "Hello Test";
}

int main()
{
  cout << test::testStr << endl;
  return 0;
}

Math

#include <cmath>
#include <iostream>

using namespace std

int main() {
  cout << max(5, 10);
  cout << min(5, 10);
  cout << sqrt(9);
  cout << round(5.6);
  cout << log(2);
}

Conditions

#include <iostream>
#include <string>

using namespace std;

int main()
{
  int x = 10;
  int y = 20;

  if (x > 10)
  {
    cout << "x greater than 10 \n";
  }
  else if (x <= 10)
  {
    cout << "x less than 10 \n";
  }

  string res = y > x ? "y greater than x" : "x greater than y";

  cout << res << "\n";

  return 0;
}

Array

#include <iostream>

using namespace std;

int main()
{
  int arr[] = {1, 2, 3, 4, 5};

  for (int i : arr)
  {
    cout << i << " ";
  }

  return 0;
}

sizeof

  • sizeof will return the array length of byte, not the array length;
#include <iostream>

int main() {
  int arr[] = {1,2,3,4,5};
  for (int i = 0; i < sizeof(arr) / sizeof(int); i++) {
    cout << arr[i] << " ";
  }

  return 0;
}

Structures

Structures (also called structs) are a way to group several related variables into one place. Each variable in the structure is known as a member of the structure.

Unlike an array, a structure can contain many different data types (int, string, bool, etc.).

#include <iostream>

using namespace std;

struct Test
{
  int myNum;
  string myString;
};

int main()
{
  Test t1;
  t1.myNum = 1;
  t1.myString = "t1";

  cout << t1.myNum << "\n"
       << t1.myString;
  return 0;
}

Creating References

A reference variable is a “reference” to an existing variable, and it is created with the & operator

#include <iostream>

using namespace std;

int main() {
  string str = "string";
  string &oldStr = str;
  str = "newString";

  cout << str + "\n" + oldStr;
}