Constants And Variables - IBM 1620 Manual

Constants and Variables
Constants
Fixed Point Constants
Floating Point Constants
Variables
14
Mathematical problems usually contain some data that does not change throughout
the entire problem, and other data that may change many times during calculation.
These two kinds of data are referred to as "constants" and "variables," respectively.
Both constants and variables can be used in
FORTRAN
if they are written so that
the processor can distinguish one from the other.
A constant is any number which is used in computations without change from one
execution of the program to the next. It appears in its actual numerical form in the
source statement. In the statement
6 is a constant because it appears in its actual numerical form. (The asterisk indi-
cates the arithmetic operation of multiplication.)
You can write constants in floating point or fixed point form.
Definition:
Example:
Definition:
Example:
A fixed point constant is written
without
a decimal point,
using the digits 0, 1, . . . 9. A preceding plus sign or minus
sign is optional. The length of the constant cannot exceed
4 digits.
o
+3
-2496
48
Any number written
with
a decimal point, using the digits
0, 1, . . . 9. A preceding plus or minus sign is optional. An
unSigned constant is assumed to be positive.
The constant may contain an exponent, The exponent, pre-
ceded by the letter E, may have a preceding plus or minus
sign.
All floating point constants are converted to an 8-digit man-
tissa with a 2-digit exponent.
Constants in input data may contain up to 20 digits, but
only the first eight significant digits will be carried in the
mantissa during calculation.
42.
1.13
.0046
5000.
6.0E3
6.0E+3
4264.44
-.00004
(6.0
X
10 3 or 6000)
(6.0 X 10 3 or 6000)
When a quantity in a
FORTRAN
problem is not constant, that is, when its value varies
for different executions of the program, or varies at different stages within the pro-
gram, it is known as a variable quantity. Variable quantities are given names so