Q.The textbook gives the following examples of declaration of variables:

int    length;  
float  area;  
char   ch;  
double density;  
int    x, y, z;  
float  p, q, array[25];  

A declaration tells the compiler the name and data type of each variable so that memory can be reserved for it before the variable is used. …

[!TLDR]

All variables must be declared before use; a declaration states the data type followed by one or more comma-separated variable names and a semicolon.

The purpose of a declaration is to reserve memory of the correct size for each variable. Its syntax is:

data_type varlist;

where data_type is a basic type (int, float, char or double) and varlist is one or more variables of that type separated by commas, ending with a semicolon. In the examples, int length; reserves an integer, float area; a floating-point number, char ch; a single character and double density; a double-precision number. Several variables of the same type can be declared together, as in int x, y, z;, and an array is declared by giving its size in brackets …