Radio Shack TRS-80 User Manual page 28

Sample Run:
25
DEGREES CELSIUS
= 77
DEGREES FAHRENHEIT.
First
notice that line
40
consists
of a
PRINT
statement-
followed by four
separate expres-
sions
—
two
variables
and two groups
of
words
in
quotes called "literals"
or "strings".
Next, note
how
the parentheses are placed in line 30.
With
the 9/5 secure inside,
we
can
multiply
its
quotient times C, then
add
32,
Now, remove the parentheses in line
30 and
RUN
again.
The answer comes out the same.
Why?
1.
On
the
first
pass,
the
Computer
started
by
solving all
problems
within parentheses,
in
this
case just
one
(9/5). It
came up
with (but did
not
print) 1.8. It
then
multiplied the
1.8 times the value of
C and added
32.
2.
On
our next
try,
without
the parentheses, the
Computer
simply
moved
from
left to
right
performing
first
the
division
problem
(9
divided
by
5),
then the multiplication
problem
(1.8
times C),
then the addition
problem
(adding
32).
The
parentheses really
made
no difference
in
our
first
example.
Next, change
+32
to
32+ and move
it
to
the front of the equation
in line 30.
Run
it
again,
without parentheses.
Did
it
make
a
difference
in
the
answer?
Why
not?
Answer: Execution proceeds from
left
to right,
multiplication
and
division
first,
then
returns
and performs
addition
and
subtraction.
This
is
why
the 32
was not
added
to
the 9
before heing divided
by
5.
Very important!
If
they
had been added,
we would of course
have gotten the
wrong
answer.
EXERCISE
5-1
:
Write
and run
a
program which
converts 65°
Fahrenheit to
Celsius.
The
rule
tells
us that "Celsius
temperature
is
equal to five-ninths
times what's
left
after
32°
is
sub-
tracted
from
the
Fahrenheit temperature."
C° = (F°-32)X
5.
9
Remember
what the semi-eol«ns are for?
26