There are four basic data types in C language. They are given as below along with number of bytes occupied by them in the computer memory (RAM).
char : It refers to character. It can hold one letter/symbol. char in C language is associated with integers to refer a letter/symbol as per ASCII (American Standard Code for Information Interchange) which has assigned integer value for all letters/symbols used in programming.
int : It refers integer. It can hold a signed or unsigned whole number within the specified range.
float : It refers floating point or real number. It can hold a real number like 3.142857 or 4.23e6 with decimal digits in decimal or exponential form. A float number using 6 decimal digits is called a single precision number.
double : It also refers to floating point or real number. It can hold a real number in double precision. A double precision number uses 12 decimal digits like 3.142857142857 or 4.23145342148e12