We have to declare all variables and constants, before we can use them. When we declare a variable, we specify its data type.
For example, to declare a variable with data type integer, float, and character, we simply write:
int sum;
float area;
char letter;
or we can group similar data type variables in one list such as:
int n1, n2, sum, diff;
float area, fah, celsius, divided;
char letter, symbol, initial;