In this formula, rate is the annual interest rate expressed as a fraction; since it is more conventional to quote interest rates as a percentage the program does this conversion for us.
PROGRAM LOAN WRITE(UNIT=*, FMT=*)'Enter amount, % rate, years' READ(UNIT=*, FMT=*) AMOUNT, PCRATE, NYEARS RATE = PCRATE / 100.0 REPAY = RATE * AMOUNT / (1.0 - (1.0+RATE)**(-NYEARS)) WRITE(UNIT=*, FMT=*)'Annual repayments are ', REPAY END |
READ and assignment
statements, both of which can be used to assign new values to variables.
The READ statement has a similar form to WRITE: here it reads in three
numbers entered on the terminal in response to the prompt and assigns their
values to the three named variables. FMT=* again selects list-directed (or
free-format) input which allows the numbers to be given in any convenient
form: they can be separated by spaces or commas or even given one on each
line.
The fourth statement is an assignment statement which divides PCRATE by 100
and assigns the result to another variable called RATE. The next assignment
statement evaluates the loan repayment formula and assigns the result to a variable
called REPAY.
Several arithmetic operators are used in these expressions: as in most
programming languages "/" represents division and "*" represents multiplication; in
Fortran "**" is used for exponentiation, i.e. raising one number to the power
of another. Note that two operators cannot appear in succession as this
could be ambiguous, so that instead of "**-N" the form "**(-N)" has to be
used.
Another general point concerning program layout: spaces (blanks) are not significant in Fortran statements so they can be inserted freely to improve the legibility of the program.
When the program is run, the terminal dialogue will look something like this:
Enter amount, % rate, years 20000, 9.5, 15 Annual repayments are 2554.873 |
