100 CLS
110 '
120 PRINT "Homework. BASIC Program: Test For Prime"
130 PRINT
140 PRINT
150 PRINT
170 PRINT "To determine whether a number is prime, please enter a number greater than 0"
180 PRINT
190 PRINT
200 INPUT "Which number would you like to test"; X
210
220 IF X = 0 THEN PRINT "Error! Your number must be larger than 0": GOTO 900
230 IF X = 1 THEN PRINT "1 is neither a prime number nor a composite number, it is the number by which   prime numbers are defined.": GOTO 900
240 IF X = 3 THEN PRINT "3 is a prime number.": GOTO 900
250 '
260     LET Y = (X / 2)
270             IF Y = 1 THEN PRINT X; "is a prime number.": GOTO 900
280                     IF Y = INT(Y) THEN PRINT X; "is not prime because it is divisible by 2.": GOTO 900
290
300
310 ' (The section above tests for even primes.  If it's not '2' or divided by 2, it must be odd.)
320 ' (The next section loops thru all the odd numbers less than the number chosen)                                           
330 '  
340 '
350     LET Q = (X - 2)
360     FOR M = 3 TO Q STEP 2
370                LET P = (X / M)
380                IF P = INT(P) THEN PRINT X; "is not prime because it is divisible by"; M: GOTO 900
390     NEXT M
400           
410 PRINT X; "is a prime number"
420
430
890 ' (End of program decision: yes,no or end)
900 PRINT
910 PRINT
920 PRINT
930 PRINT "Would you like to try again? (Y/N)"
940 INPUT A$
950 IF A$ = "Y" THEN GOTO 180
960 PRINT
970 PRINT
980 PRINT "This completes our test of the emergency prime number testing system. If this   had been an actual prime number emergency, you would have been directed to the nearest mathematics textbook."
990 PRINT "Thank you and good day."
999 END