Fortran Variable Declarations

Declaring the type of a Fortran variable is done with type statements. It has the following form:

type-specifier :: list

where the type-specifier is one of the following and list is a list of variable names separated with commas:

INTEGER : the variables in list can hold integers
REAL: the variables in list can hold real numbers
COMPLEX: the variables in list can hold complex numbers
LOGICAL: the variables in list can hold logical values (i.e., true or false)
CHARACTER: the variables in list can hold character strings

Types INTEGER and REAL are easy. The following are examples:

Variables ZIP, Mean and Total are of type INTEGER:
```
INTEGER :: ZIP, Mean, Total
```
Variables Average, error, sum and ZAP are of type REAL:
```
REAL  ::  Average, error, sum, ZAP
```

Type CHARACTER is more involved. Since a string has a length attribute, a length value must be attached to character variable declarations. There are two ways to do this:

Use CHARACTER(LEN=i) to declare character variables of length i. For examples,
- Name and Street are character variables that can hold a string of no more than 15 characters:
```
CHARACTER(LEN=15) :: Name, Street
```
- FirstName, LastName and OtherName are character variables that can hold a string of no more than 20 characters:
```
CHARACTER(LEN=20) :: FirstName, LastName, OtehrName
```
Use CHARACTER(i) to declare character variables of length i. That is, there is no LEN= in the parenthesis. For examples,
- Name and Street are character variables that can hold a string of no more than 15 characters:
```
CHARACTER(15) :: Name, Street
```
- FirstName, LastName and OtherName are character variables that can hold a string of no more than 20 characters:
```
CHARACTER(20) :: FirstName, LastName, OtehrName
```
If a variable can only hold a single character, the length part can be removed. The following three declarations are all equivalent:
```
CHARACTER(LEN=1)  :: letter, digit
CHARACTER(1)      :: letter, digit
CHARACTER         :: letter, digit
```
Here, variables letter and digit can only hold no more than one character.

If you want to declare character variables of different length with a single statement, you can attach a length specification, *i, to the right of a variable. In this case, the corresponding variable will have the indicated length and all other variables are not affected.
```
CHARACTER(LEN=10) :: City, Nation*20, BOX, bug*1
```
Here, variables City and BOX can hold a string of no more than 10 characters, Nation can hold a string of no more than 20 characters, and bug can hold only one character.

There is one more way of specifying the length of a character variable. If the length value is replaced with a asterisk *, it means the lengths of the declared variables are determined elsewhere. In general, this type of declarations is used in subprogram arguments or in PARAMETER and is refereed to as assumed length specifier.
```
CHARACTER(LEN=*) :: Title, Position
```
Here, the actual lengths of variables Title and Position are unknown and will be determined elsewhere.