C++ – Variables and Datatypes

C++ – Variables and Datatypes

Variables let you store values dynamically.

Declare a variable

First you have to declare the variable type, the most used are:

Character types
– char Exactly one byte in size. At least 8 bits.
– char16_t Not smaller than char. At least 16 bits.
– char32_t Not smaller than char16_t. At least 32 bits.
– wchar_t Can represent the largest supported character set.

Integer types (signed)
– signed char Same size as char. At least 8 bits.
– signed short int Not smaller than char. At least 16 bits.
– signed int Not smaller than short. At least 16 bits.
– signed long int Not smaller than int. At least 32 bits.
– signed long long int Not smaller than long. At least 64 bits.

Integer types (unsigned) Same size as their signed counterparts
– unsigned char
– unsigned short int
– unsigned int
– unsigned long int
– unsigned long long int

Floating-point types
– float
– double Precision not less than float
– long double Precision not less than double

Boolean type
– bool

Void type
– void no storage

Null pointer
– decltype(nullptr)

Declaration of variables sample:

#include <iostream>
using namespace std;

int main ()
{
  // declaring variables:
  int a, b;
  int result;

  // process:
  a = 5;
  b = 2;
  a = a + 1;
  result = a - b;

  // print out the result:
  cout << result;

  // terminate the program:
  return 0;
}

Initialization

Initialization of variables, the initial value of a variable:

#include <iostream>
using namespace std;

int main ()
{
  // initialization of variables
  int a=5;               // initial value: 5
  int b(3);              // initial value: 3
  int c{2};              // initial value: 2
  int result;            // initial value undetermined

  a = a + b;
  result = a - c;
  cout << result; // the result is 6

  return 0;
}

Type deduction: auto and decltype

// auto
int foo = 0;
auto bar = foo;  // the same as: int bar = foo; 

//decltype
int foo = 0;
decltype(foo) bar;  // the same as: int bar;