Declaration of variables

In order to use a variable in C++, we must first declare it specifying which data type we want it to be. The syntax
to declare a new variable is to write the specifier of the desired data type (like int, bool, float...) followed by a valid
variable identifier. For example:
int a;
float mynumber;
These are two valid declarations of variables. The first one declares a variable of type int with the identifier a. The
second one declares a variable of type float with the identifier mynumber. Once declared, the variables a and
mynumber can be used within the rest of their scope in the program.
If you are going to declare more than one variable of the same type, you can declare all of them in a single
statement by separating their identifiers with commas. For example:
int a, b, c;
This declares three variables (a, b and c), all of them of type int, and has exactly the same meaning as:
int a;
int b;
int c;
The integer data types char, short, long and int can be either signed or unsigned depending on the range of
numbers needed to be represented. Signed types can represent both positive and negative values, whereas
unsigned types can only represent positive values (and zero). This can be specified by using either the specifier
signed or the specifier unsigned before the type name. For example:
unsigned short int NumberOfSisters;
signed int MyAccountBalance;
By default, if we do not specify either signed or unsigned most compiler settings will assume the type to be
signed, therefore instead of the second declaration above we could have written:
int MyAccountBalance;
with exactly the same meaning (with or without the keyword signed)
An exception to this general rule is the char type, which exists by itself and is considered a different fundamental
data type from signed char and unsigned char, thought to store characters. You should use either signed or
unsigned if you intend to store numerical values in a char-sized variable.
short and long can be used alone as type specifiers. In this case, they refer to their respective integer
fundamental types: short is equivalent to short int and long is equivalent to long int. The following two
variable declarations are equivalent:
short Year;
short int Year;
Finally, signed and unsigned may also be used as standalone type specifiers, meaning the same as signed int
and unsigned int respectively. The following two declarations are equivalent:
unsigned NextYear;
unsigned int NextYear;
To see what variable declarations look like in action within a program, we are going to see the C++ code of the
example about your mental memory proposed at the beginning of this section:
// operating with variables
#include <iostream>
using namespace std;
int main ()
{
// declaring variables:
int a, b;
int result;
// process:
a = 5;
b = 2;
a = a + 1;
result = a - b;
// print out the result:
cout << result;
// terminate the program:
return 0;
}
4
Do not worry if something else than the variable declarations themselves looks a bit strange to you. You will see
the rest in detail in coming sections.