page-1983-101-timex-sinclair-programming-tricks

100 PRINT •BACKWARD, IT IS •;R105 PAUSE 200110 GOTO 10l45 Number Reverser IIGive the computer a number. It will immediately,display the number printed backward on the videodisplay.Line 20 collects the number from you. Line 30measures its length. Lines 40-70 reverse it and line 80displays the reversed number.Program Listing10 LET B$= 0 •20 PRINT 0 GIVE ME A NUMBER •;25 INPUT N$30 LET L=LEN N$35 PRINT N$40 FOR Y=L TO 1 STEP -150 LET B$=B$+N$(Y)60 NEXT Y70 LET B=VAL B$80 PRINT 0 REVERSED, THE NUMBER IS •;B90 PRINT100 GOTO 1046 Number-Error TrappingGood programs, those which are well written, neederror trapping. It's a technique for making sure personscommunicating with the computer don't key in inappropriatedata or make mistakes which would cause computationproblems for the computer.For instance, see the example program here. In line65