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The WHILE construct
The general structure of this command is:
WHILE logical_statement REPEAT program_statements END
The WHILE statement will repeat the program_statements while
logical_statement is true (non zero). If not, program control is passed to
the statement right after END. The program_statements must include a
loop index that gets modified before the logical_statement is checked at
the beginning of the next repetition. Unlike the DO command, if the first
evaluation of logical_statement is false, the loop is never executed.
Example 1
– calculate the summation S using a WHILE…REPEAT…END
construct
The following program calculates the summation
Using a WHILE…REPEAT…END loop:
« 0. → n S « WHILE ‘n≥0‘ REPEAT n SQ S + ‘S‘ STO n 1 – ‘n‘ STO
END S “S” →TAG » »
Store this program in a variable @@S4@@. Verify the following exercises: J
3 @@@S4@@ Result: S:14 4 @@@S4@@ Result: S:30
5 @@@S4@@ Result: S:55 8 @@@S4@@ Result: S:204
10 @@@S4@@ Result: S:385 20 @@@S4@@ Result: S:2870
30 @@@S4@@ Result: S:9455 100 @@@S4@@ Result: S:338350
Example 2
– generate a list using a WHILE…REPEAT…END construct
Type in the following program
« → xs xe dx « xe xs – dx / ABS 1. + xs → n x « xs WHILE
‘x<xe‘ REPEAT ‘x+dx‘ EVAL DUP ‘x‘ STO END n →LIST » » »
∑
=
=
n
k
kS
0
2
