Fortran 90 Tutorial

6. Loops

DO loops may have either of the two forms:
```
   DO index variable = start, end, step
       statements
   END DO
```
or,
```
   DO n index variable = start, end, step
       statements
   n CONTINUE
```
In both cases, the step variable is optional and is assumed to have the value 1 if omitted. As with IF-ELSE and CASE constructs, DO loops may also have names.

WHILE loops are allowed. They have the general form:

   DO WHILE (logical argument)
      statements
   END DO

An "infinite" loop may be performed as follows:
```
   DO
      .
      .
      .

      conditional statement EXIT
      .
      .
      .

   END DO
```
In this instance, a set of statements are executed repetitively until the conditional statement is satisfied. When this occurs, program control jumps to the next executable statement following the END DO.

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