Numbers in

About Numbers

The built-in number types in C++ can be divided into integers and floating points. Integers are whole numbers like 0, 691, or -2. Floating point numbers are numbers with a decimal point like 6.02214076, 0.1, or -1.616.

Integers

The following example shows the declaration and initialization of four different variables

int m_morales{9241};              // base 10: 0-9
int a_apaec{0x24CD};              // base 16: 0-9 and A-F
int m_gargan{0b10010000011001};   // base  2: 0-1
int b_reilly{022031};             // base  8: 0-7
                                  // Leading with a 0 not the letter o.

When you assign a value to an int variable, you can do so directly with a literal. A literal is a hard-coded number like 9241. There are different integer literals for several bases of the representation. Decimal integer literals are the most common and use the digits 0 to 9. By adding a special prefix, like 0x, it is possible to use other bases. The example above shows the number 9421 in its four representations and prefixes. All variables are initialized to the same value.

For more details on the different representation systems, take a look at a small tutorial.

You can use an apostrophe to separate digits for easier readability. 9'241 is the same as 0b0100'100'0001'1001 or 92'4'1.

Floating-Point Numbers

The floating-point literals come in two flavors. In addition to the intuitive 0.0024 it is possible to use its scientific notation 2.4e-3. The most common floating-point type is double.

Arithmetic

C++ supports +, -, *, /, ( and ) and % to form expressions. The result from the operation between two integers is also an integer. 5 / 2 will return 2. When one of the involved types is a floating-point type, the result will also be of a floating-point. 5.0 / 2 and 5 / 2.0 will return 2.5. % is the remainder operator and will return the remainder of an integer division: 5%3 is 2.

Assignment operator

The assignment operator assigns a variable with a literal. Always takes place from right to left, and never the other way around.

int length = 5;
int width = 2;
length = width;

Here integer value 5 is assigned to the variable length. Then integer value 2 is assigned to variable width. Finally value of width is copied to the variable length and the earlier value 5 will be lost. Consider also that we are only assigning the value of width to length at the moment of the assignment operation. Therefore, if the value of width changes at a later moment, it will not affect the value taken by length.

Assignment operator can be combined with the other operators(arithmetic & bitwise) known as compound assignment operators +=, -=, *=, /=, %=. These operators modify the current value of a variable by performing an operation on it.

// we start with 0 people
int people{};
// we need 0 eggs
int eggs{}; 
// two people joined:
people += 2; 
// people is now 2
// let's add 3 eggs per person
eggs += 3 * people;
// eggs is now 6

Variables people & eggs are initialized to 0. Then, we add integer value 2 over the existing value 0 of the variable people and assign it back to people. people becomes 2 now. Later, we add 3 eggs for each person, which turns out to be 6 eggs in total. Now add this 6 to existing value 0 of the variable eggs and assign it back to eggs. eggs will be 6 now. The equivalent expression would be people = people + 2 and eggs = eggs + (3 * people).

double pi{3.14};
int about_2_times_pi_cpp{static_cast<int>(pi) * 2};
// Old C-style cast:
int about_2_times_pi_c{(int)pi * 2};