Variable. The information stored inside an object is called as a value. Of course the machine itself typically has no idea how to interpret the information it contains, but the program certainly needs to know. For this reason a variable has a specific type. And it's this type that constrains the use of that variable, such that only operations appropriate to the type may be performed. Any variable in C language acts like a container of data. C variables can be changed as per the requirement of the user and can be represented by any datatype like int, char, float, etc. C language variables are categorized into three groups.
letters(all alphabets a to z & A to Z) and
digits(all digits 0 to 9) but must begin with a letter only.
case sensitivewith lowercase letters typically used for variable names, and uppercase for constants.