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The type of a variable determines how much space it occupies in storage and how the bit pattern stored is interpreted. Standard data types in C are listed in the following table:
| Variable Type | Keyword | Range | Storage in Bytes |
|---|---|---|---|
| Character | char | -127 to 127 | 1 |
| Unsigned character | unsigned char | 0 to 255 | 1 |
| (Signed) integer | int | -32,768 to 32,767 | 2 |
| Unsigned integer | unsigned int | 0 to 65,535 | 2 |
| Short integer | short | -32,768 to 32,767 | 2 |
| Unsigned short integer | unsigned short | 0 to 65,535 | 2 |
| Long integer | long | -2,147,483,648 to 2,147,483,647 | 4 |
| Unsigned long | integerunsigned long | 0 to 4,294,967,295 | 4 |
| Single precision floating point | float | 1.2E-38 to 3.4E38, approx. range precision = 7 digits. | 4 |
| Double precision floating point | double | 2.2E-308 to 1.8E308, approx. range precision = 19 digits. | 8 |
Variables
A variable is an object of a specified type whose value can be changed. In programming languages, a variable is allocated a storage location that can contain data that can be modified during program execution. Each variable has a name that uniquely identifies it within its level of scope.
In C, a variable must be declared before use , although certain declarations can be made implicitly by content. Variables can be declared at the start of any block of code, but most are found at the start of each function. Most local variables are created when the function is called, and are destroyed on return from that function.
A declaration begins with the type, followed by the name of one or more variables. Syntax of declare statement is described as:
data_type list_of_variables;
A list of variables includes one or many variable names separated by commas.
Single declarations
int age; //integer variable
float amountOfMoney;//float variablechar initial;// character variable
Multiple declarations:
int age, houseNumber, quantity;
float distance, rateOfDiscount;char firstInitial, secondInitial; Variables can also be initialized when they are declared, this is done by adding an equals sign and the required value after the declaration.
int high = 250; //Maximum Temperature
int low = -40; //Minimum Temperatureint results[20]; //Series of temperature readings Constants
A constant is an object whose value cannot be changed. There are two method to define constant in C:
#define constant_name value
#define MAX_SALARY_LEVEL 15 //An integer constant
#define DEP_NAME “Computer Science”// A string constant const data_type variable_name = value;
const double e = 2.71828182845905; Usually i/o, input and output, form the most important part of any program. To do anything useful your program needs to be able to accept input data and report back your results. In C, the standard library (stdio.h) provides routines for input and output. The standard library has functions for i/o that handle input, output, and character and string manipulation. Standard input is usually means input using the keyboard. Standard output is usually means output onto the monitor.
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