C++ - Chapter 2 - Variables
Introduction
Remember math? 3 + 5 = x? If you've passed 2nd grade, you'll know that x=8, right? In this example x is a variable. You will use variables significantly in all programming languages. You can use a variable to store a username, an identification number, the amount of money you have--what ever you choose. You can also use variables to calculate additional variables. Let's look deeper...
Definitions (in layman's terms)
Variables are storage bins in the computer's memory for you to store, retrieve, and manipulate data.
Arithmetic Operators are used to perform mathematic operations on variables.
| Operator | Operation |
| + | addition |
| - | subtraction |
| * | multiplication |
| / | division |
| % | modulo division |
Type Specifiers are special keywords used to define the type of data that is to be stored in a variable.
| Type Specifier | Variable Type | Bytes Used | Values |
| int | integers | 4 | -2,147,483,648 to 2,147,483,687 |
| double | floating point numbers | 8 | 1.7E (+/-)308 |
| bool | logical values | 1 | true or false |
| char | characters | 1 | -127 to 128 |
| Type Specifier | Variable Type | Bytes Used | Values |
| short int | integers | 2 | -32,768 to 32,767 |
| unsigned short int | integers | 2 | 0 to 65,535 |
| unsigned int | integers | 4 | 0 to 4,294,967,295 |
| long int | integers | 4 | –2,147,483,648 to 2,147,483,647 |
| unsigned long int | integers | 4 | 0 to 4,294,967,295 |
| float | floating point numbers | 4 | 3.4E (+/-)38 |
| long double | floating point numbers | 8 | 1.2E (+/-)4932 |
| unsigned char | characters or bytes | 1 | 0 to 255 |
Code:
#include <iostream>
using namespace std;
int main (void)
{
cout<<"Hello World!"<<endl<<endl;
return 0;
}
Breakdown
int x, y; is called an initialization line. This line of code specifies that there are two variables named x and y and both are of type int.
x = 3; stores the value "3" into the variable x. When storing a value into a variable container, the variable must always be on the left hand side and the value on the right. For instance, 3 = x is incorrect.
int a = x + y; shows that you can initialize a variable in-line as well as perform arithmetic on the variables. This line initializes a variable of type "int", named "a", and assigns it a value of "8" (3 + 5).
// addition is called an in-line comment. These are not interpreted by the compiler, but are useful for any humans (including yourself) who read and try to interpret your source code. It is always a good idea to comment your source code so you can know what's going on if you ever have to edit your code later.
Code:
#include <iostream>
using namespace std;
int main (void)
{
int a = 3, b = 7;
int k, l, m, n, p;
double o;
k = b + a; // addition (7 + 3) = 10
l = b - a; // subtraction (7 - 3) = 4
m = b * a; // multiplication (7 * 3) = 21
n = b / a; // division (7 / 3) = 2
o = (double)b / (double)a // division (7.0 / 3.0) = 2.33333
p = b % a; // modulo (7 % 3) = 1
cout<<"k = "<<k<<endl;
cout<<"l = "<<l<<endl;
cout<<"m = "<<m<<endl;
cout<<"n = "<<n<<endl;
cout<<"o = "<<o<<endl;
cout<<"p = "<<p<<endl;
return 0;
}
Output
k = 10 l = 4 m = 21 n = 2 o = 2.333333 p = 1
Breakdown
Notice that when you store the division of two numbers as an integer, the fractional component is truncated. This means that only the whole-number (integer) part is used and fractional parts are neglected. Inserting the (double) modifier before a variable is called type-casting. This casts the variable into a new memory type. This is done to prevent what is referred to as mixed-mode operation. Avoid mixed-mode operations if at all possible as it leads to loss of precision in the values. Storing the division into a double value preserves the fractional component as can be seen by the variable "o".
When you perform a modulo divide, you are computing the remainder of a division. For instance 10 % 6 = 4. 4 is the remainder of 10 divided by six. The modulo operator only works on integer data types.
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