Below is a code to create a calculator program in Qbasic that asks the user to enter 2 numbers and then asks the user to choose from options to add, subtract, multiply or divide the two numbers. Input validation has to be used in this code to identify if the user has entered the correct data. This program will also ask users to continue or exit in the end after the results.
1 CLS
COLOR 7
DIM NUM1 AS SINGLE
DIM NUM2 AS SINGLE
PRINT TAB(30); "BASIC CALCULATOR "
DO WHILE REP$ <> "N"
PRINT
INPUT "FIRST NUMBER"; NUM1
PRINT
INPUT "OPERATOR"; OPERATOR$
PRINT
INPUT "SECOND NUMBER"; NUM2
PRINT
CALL OPERAN(NUM1, OPERATOR$, NUM2) 'FOR OPERATORS
INPUT "TO EXIT PRESS (N), TO CONTINUE PRESS ENTER"; REP$
REP$ = UCASE$(REP$)
GOTO 1
LOOP
COLOR 4
SUB OPERAN (NUM1, OPERATOR$, NUM2)
COLOR 2
PRINT NUM1; OPERATOR$; NUM2; "=";
IF OPERATOR$ = "+" THEN
PRINT NUM1 + NUM2
ELSE IF OPERATOR$ = "-" THEN
PRINT NUM1 - NUM2
ELSE IF OPERATOR$ = "*" THEN
PRINT NUM1 * NUM2
ELSE IF OPERATOR$ = "/" THEN
PRINT NUM1 / NUM2
ELSE
COLOR 4
PRINT " YOU HAVED ENTERED A WRONG OPERATOR SIGN"
BEEP
END IF
END IF
END IF
END IF
PRINT
CALL FOOTB
END SUB
SUB FOOTB
COLOR 4
COLOR 7
END SUB