IBM SC34-5764-01 Manual do Utilizador descarregar pdf (Página 67)

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101

Exercise - Using a DO UNTIL Loop

Change the program in the previous exercise on page “Exercise - Using a DO WHILE Loop” on page 43

from a DO WHILE to a DO UNTIL loop and achieve the same results. Remember that DO WHILE loops

check for true expressions and DO UNTIL loops check for false expressions, which means their logical

operators are often reversed.

/******************************** REXX ******************************/

/* This program uses a DO UNTIL loop to ask for a password. If the */

/* password is incorrect three times, the loop ends. */

/********************************************************************/

password = 'abracadabra'

time = 0

DO UNTIL (answer = password) | (time = 3)

PULL answer /* Gets ANSWER from input stream */

time = time + 1

END

Figure 24. Example Using DO UNTIL

Control Flow within a Program

Chapter 4. Controlling the Flow within a program 45

1 2 ... 62 63 64 65 66 67 68 69 70 71 72 ... 480 481

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