0 REM "prime-no.bas"
1 CLS : PRINT "          PRIME NUMBER TESTING PROGRAM"
2 PRINT "               by Phillip Bigelow"
3 PRINT : PRINT : PRINT : PRINT "This program can test numbers from one through 16 digits long."
4 PRINT "(testing numbers of 17 digits or more gives unreliable results due to":PRINT "round-off error)":PRINT:PRINT "Note: The computer will appear to hang when large numbers"
5 PRINT "are tested."
6 PRINT "Don't let the long delay upset you! The program is working!"
9 PRINT "Very large numbers can require a few hours to a few days to test.": PRINT : PRINT
10 PRINT : INPUT "What is the number that you want to test";Q#
11 CLS
12 PRINT "Program is now running...To stop program, hold down the Ctrl key while pressing the Pause key"
14 PRINT : PRINT : PRINT "Testing number"; Q#;"         Please wait.":IF Q#>9999999999999999# THEN 200
15 PRINT : PRINT : PRINT
16 LET B$=TIME$
17 LET X#=2#
20 LET Y#=Q#/X#
21 IF Q#=1 THEN 50
22 IF Q#=2 THEN 50
34 IF Y#=INT(Y#) THEN CLS:IF Y#=INT(Y#) THEN PRINT "--------------------------RESULTS-------------------------"
35 IF Y#=INT(Y#) THEN PRINT "The number"; Q#; "is NOT prime": PRINT
36 IF Y#=INT(Y#) THEN PRINT "divisible by", X#
38 IF Y#=INT(Y#) THEN 52
39 IF Y#=INT(Y#) THEN 100
41 LET X#=X#+1
42 IF X#>INT((Q#/2)+1) THEN 50
45 GOTO 20
50 CLS:PRINT "-------------------------RESULTS--------------------------"
51 PRINT "YOU HAVE A WINNER!", Q#; "IS A PRIME NUMBER!!!"
52 PRINT "Calculation began at = ";B$
53 PRINT "Calculation ended at = ";TIME$
54 PRINT "----------------------------------------------------------"
55 PRINT
56 IF Y#=INT(Y#) THEN 39
57 REM Copyright Hell Creek Life, 2009 Phillip Bigelow
100 PRINT "                MENU":PRINT "Test another number (t), or exit to system/Windows (x)":JH$=INPUT$(1)
101 IF JH$="t" THEN 1
102 IF JH$="x" THEN SYSTEM
103 CLS:GOTO 100
200 PRINT:PRINT:BEEP:BEEP:BEEP:PRINT "Error: GWBASIC/QBASIC cannot accurately determine whether a number"
201 PRINT "over 16 digits is a prime number.  Please choose another number to test.":GOTO 10