Answer:

> — greater than

' Add up numbers that the user enters.
' When the user enters any negative number, 
' print the sum and end the program.
'
LET SUM = 0
'
PRINT "Enter a positive number"       
INPUT NUMBER                 
'
DO WHILE NUMBER > 0
  LET SUM = SUM + NUMBER   
  PRINT "Enter a positive number."       
  INPUT NUMBER                 
LOOP
'
PRINT "The sum is", SUM
END

A Scheme for `DO WHILE` loops

Here is an outline of the above program. The program will do "something or other" until a sentinel value is entered.


. . . . do beginning things . . . 

PRINT "Enter first number"       
INPUT NUMBER                 
'
DO WHILE ... number is not a sentinel value ...
 
  . . . do something or other . . .    
 
  PRINT "Enter the next number."       
  INPUT NUMBER                 
LOOP

. . . . do ending things . . . .
END

To change this scheme into a program you have to decide what you want to do, and decide how to fill in the blanks in this scheme to do it. Sometimes a blank needs to be filled with many statements; sometimes with none.

You want a program that repeatedly computes the square root of numbers the user types in. In QBasic SQR ( NUMBER ) is the square root of NUMBER. Since negative numbers don't have square roots, you want any negative number to act as a sentinel. You expect the monitor screen to look something like:

Enter the first number
? 3
Square root is:  1.7320508
Enter the next number
? 4
Square root is:  2
Enter the next number
? -10
Bye

QUESTION 16:

Look at the scheme DO WHILE programs. To start out, decide what to do with the blanks:

. . . . do beginning things . . .

and

. . . . do ending things . . . .

The remaining blanks will be left until later.

Answer:

A Scheme for DO WHILE loops

QUESTION 16:

A Scheme for `DO WHILE` loops