Variabels in C

•  A variable is a name of the memory location. It is used to store data. Its value can be changed, and it can be reused many times.

• It is a way to represent memory location through symbol so that it can be easily identified.

• To manipulate memory address easily, we can attach a variable name to the memory address.

• So, it will be very easier to manipulate the memory address using a variable name rather than hexadecimal values.

• Datatype variable_name;  

Rules for Defining a Variable

1.  variable can have alphabets, digits, and underscore.

• valid: abc, ab1, _abc;
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2. A variable name can start with the alphabet, and underscore only. It can't start with a digit.

• valid: var, _value, name;
• Invalid: 1var, 23cr;
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3. Variables are also case sensitive. 

• Age and age is different variables.
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4. No whitespace is allowed within the variable name.

• valid: abc, variable_name;
• Invalid: variable name, hel lo;
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5.A variable name must not be any reserved word or keyword, e.g. int, float, main