C Variables And Constants

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Variables are containers for storing data values, like numbers and characters.

Declaring (Creating) Variables

To create a variable, specify the C Data Types and assign it a value:

Syntax

type variableName = value;

You can also declare a variable without assigning the value, and assign the value later:

// Declare a variable  
int myNum;  
  
// Assign a value to the variable  
myNum = 15;

Variable Names

All C variables must be identified with unique names, these unique names are called identifiers.

Naming Rules:

1. A variable name can only have letters (both uppercase and lowercase letters), digits and underscore.
2. The first letter of a variable should be either a letter or an underscore.

Output Variables

You learned from C Print Output that you can output values/print text with the printf() function:

In many other programming languages, you would normally use a print function to display the value of a variable. However, this is not possible in C:

int myNum = 15;  
printf(myNum);  // Nothing happens

To output variables in C, you must get familiar with something called “C Format Specifiers

Syntax

printf("format specifier", variable );

Change Variable Values

Note: If you assign a new value to an existing variable, it will overwrite the previous value:

int myNum = 15;  // myNum is 15  
myNum = 10;  // Now myNum is 10

Assign Values

You can also assign the value of one variable to another:

int myNum = 15;  
  
int myOtherNum = 23;  
  
// Assign the value of myOtherNum (23) to myNum  
myNum = myOtherNum;  
  
// myNum is now 23, instead of 15

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Constants

If you want to define a variable whose value cannot be changed, you can use the const keyword. This will create a constant. For example,

const double PI = 3.14;

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