Radio Shack TRS-80

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