Variables Initialization

A variable can be considered as a box that can hold a single value. However, initially the content of a variable (or a box) is empty. Therefore, before one can use a variable, it must receive a value. Do not assume the compiler or computer will put some value, say 0, into a variable. There are at least three ways to put a value into a variable:

initializing it when the program is run
using an assignment statement
reading a value from keyboard or other device with a READ statement.

The way of initializing a variable is very similar to the use of PARAMETER attribute. More precisely, do the following to initial a variable with the value of an expression:

add an equal sign (=) to the right of a variable name
to the right of the equal sign, write an expression. It is important to note that all names in the expression must constants or names of constants.

Initializing a variable is only done exactly once when the computer loads your program into memory for execution. That is, all initializations are done before the program starts its execution. The use of un-initialized variables may cause unexpected result.

Examples:

The following example initializes variables Offset to 0.1, Length to 10.0, and tolerance to 1.E-7.
```
REAL :: Offset = 0.1, Length = 10.0, tolerance = 1.E-7
```
The following example initializes variables State1 to "MI", State2 to "MN", and State3 to "MD".
```
CHARACTER(LEN=2) :: State1 = "MI", State2 = "MN", State3 = "MD"
```
The following example first defines three named integer constants with PARAMETER and uses these values to initialize two integer variables. Thus, variables Pay and Received are initialized to have values 4350 (=10*435) and 8 (3+5), respectively.
```
INTEGER, PARAMETER :: Quantity = 10, Amount = 435, Period = 3
INTEGER            :: Pay = Quantity*Amount, Received = Period+5
```
The following example contains a mistake. While the compiler is processing the initialization value for variable Received, the value of Period is unknown, although it will be defined on the next line.
```
INTEGER, PARAMETER :: Quantity = 10, Amount = 435
INTEGER            :: Pay = Quantity*Amount, Received = Period+5
INTEGER, PARAMETER :: Period = 3
```