IBM 1620 - IF Statement for Conditional Logic

IF Statement
IF (SENSE SWITCH)
Statement
The IF statement permits you to transfer the program to a particular statement
depending upon the value of an expression.
Format:
Example:
"IF (a) n
1
, n
2
, n/'
where a is an expression and n
j
n
z
and n,1 are statement
numbers.
The expression must be enclosed in parentheses. The state-
ment numbers must be separated from each other by com-
mas.
IF (A - B) 10, 5, 7
IF (A(I)/D) 1,2,3
The program is transferred to statement number n
1
, n
z
,
n;J, depending upon
whether the value of the expression a is less than, equal to, or greater than zero,
respectively.
In the first example, if both A and B have the value of 2, the program is
transferred to
statement number 5. In the second example, if the result of the
expression is greater than zero, the program is transferred to statement number 3.
Suppose a value, HRS, is being computed. Whenever this value is positive,
the main routine of the program should be followed. Whenever the value of
HRS is negative, an alternative routine starting at statement 12 is to be followed,
and if HRS is zero, an error routine at statement 72 is to be followed. This prob-
lem
can be written as follows:
STATEMENT
NUMBER
FORTRAN STA TEMENT
I
5
6
7
10 15
20 25 30 35
40
45
50 55
--
•
I I
I
, , ,
I I
L-~. _____ 1 __
•
I I
_L ... _
HRS=,( B+C)
/ (D**E)- F
----L-. _____ ...L ______ ..L........
IF
~LH R 5 ) 1
1
2, 72.r 1 0
I 1 1 I 1
------L_~
•
I 1
,
------L.....
•
_I
1
I
I
I
I
I
I
I
~-
10
•
1 I
I
.1_~_~_
•
.1. 1
-'-
~-~~~~
12
~ I I
I
I
I I
I
~~~~.~
•
,
I
I
I
I
•
I
,
........J_~~_......L~
72
•
L 1 .1. L
L~~~ __ l~
I 1
I I I
I
I
I
I
I
This statement permits the program to transfer to a particular statement depend-
ing upon the setting of anyone of the four console program switches.
Format:
Example:
"IF (SENSE SWITCH i) n
1
,
n/'
where i is the number of one of the console program
switches, and n
1
and n
z
are statement numbers.
The parentheses, enclosing the words SENSE SWITCH, and
the commas, separating the statement numbers, are required
punctuation.
IF (SENSE SWITCH 3) 14, 50
IF (SENSE SWITCH 1) 20, 40
Writing the 1620 FORTRAN Program 25