Variables are containers for storing data values.
In C, there are different types of variables (defined with different keywords), for example:
int- stores integers (whole numbers), without decimals, such as 123 or -123
float- stores floating point numbers, with decimals, such as 19.99 or -19.99
char- stores single characters, such as 'a' or 'B'. Char values are surrounded by single quotes
Declaring (Creating) Variables
To create a variable, specify the type and assign it a value:
Where type is one of C types (such as
variableName is the name of the variable (such as x or
myName). The equal sign is used to assign a value to the variable.
So, to create a variable that should store a number, look at the following example:
Create a variable called myNum of type
int and assign the value 15
You can also declare a variable without assigning the value, and assign the value later:
myNum = 15;
Note: If you assign a new value to an existing variable, it will overwrite the previous value:
myNum = 10; // Now myNum is 10
You learned from the output chapter that you can output values/print text with the
printf(myNum); // Nothing happens
To output variables in C, you must get familiar with something called "format specifiers".
Format specifiers are used together with the
function to tell the compiler what type of data the variable is storing. It is
basically a placeholder for the variable value.
A format specifier starts
with a percentage sign
%, followed by a character.
For example, to output the value of an
you must use the format
surrounded by double quotes,
printf("%d", myNum); // Outputs 15
To print other types, use
int myNum = 5; // Integer (whole number)
float myFloatNum = 5.99; // Floating point number
char myLetter = 'D'; // Character
// Print variables
To combine both text and a variable, separate them with a comma inside the
printf("My favorite number is: %d", myNum);
To print different types in a single printf() function, you can use the following:
char myLetter = 'D';
printf("My number is %d and my letter is %c", myNum, myLetter);
You will learn more about Data Types in the next chapter.
Add Variables Together
To add a variable to another variable, you can use the
int y = 6;
int sum = x + y;
Declare Multiple Variables
To declare more than one variable of the same type, use a comma-separated list:
printf("%d", x + y + z);
You can also assign the same value to multiple variables of the same type:
x = y = z = 50;
printf("%d", x + y + z);
C Variable Names
All C variables must be identified with unique names.
These unique names are called identifiers.
Identifiers can be short names (like x and y) or more descriptive names (age, sum, totalVolume).
Note: It is recommended to use descriptive names in order to create understandable and maintainable code:
int minutesPerHour = 60;
// OK, but not so easy to understand what m actually is
int m = 60;
The general rules for naming variables are:
- Names can contain letters, digits and underscores
- Names must begin with a letter or an underscore (_)
- Names are case sensitive (
myvarare different variables)
- Names cannot contain whitespaces or special characters like !, #, %, etc.
- Reserved words (such as
int) cannot be used as names