Radio Shack TRS-80 Model 100 Basic Manual page 38

How the simple interest program works:
Line
18
assigns the value of 10000 to the variable P. This is called an
assignment
statement. The letter P is called a numeric variable because numerical values can be
assigned to it. Note that the principal, $10,000, is written without the dollar sign ($)
or comma (,). In general, numeric constants should be written without commas or
dollar signs in BASIC.
Line 28 assigns the value of .18 to the variable R. This is the decimal equivalent of
the 18% interest rate. The conversion to decimal form is necessary because BASIC
does not allow numeric constants to be written with a percent (%) symbol.
Line
38
assigns the value of 10 to the variable T. This is the length of time (10 years)
allowed to repay the loan.
Line
48
computes the sum of principal and interest and assigns it to the variable S.
Note that the expression,
P
*
(1
+
R
*
T),
looks very much like the formula previously seen for calculating the sum. The symbol
"*,,
is used to denote multiplication and, as usual,
+
denotes addition.
Line 58 prints an explanatory message and the value of S.
The variables P, R, T and S are all valid examples of numeric variables. A numeric
variable can be
a) any letter
b) any two letters
or
c) a letter followed by a number.
For example, the following are all valid numeric variables:
A AA
B2
CQ
Y9
But the following are not valid numeric variables:
IS
$5
A?
"
*
I
The ftrst four lines of the program are assignment statements. In general, an
assignment statement follows the form:
variable
=
expression
where
"variable" is any valid numeric variable and "expression" is any valid
numeric expression. The right hand side can be a constant. The value of the
expression is assigned to the variable.
The arithmetic operators in BASIC are:
+
addition
subtraction
multiplication
division
exponentiation
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