i sticked to +,-,* and /. My next step is adding buttons...

notting to say...

                                    ` This code was downloaded from The Game Creators
                                    ` It is reproduced here with full permission
                                    ` http://www.thegamecreators.com
                                    
                                    `******************************************************
`                        calculator
`******************************************************

sync on

restart:
a$=""
s=0
do

	cls
	a$=a$+returnnr()
	if scancode()=14 then a$=""
	text 50,50,a$
	if returnkey()=1 then goto calc

	sync
loop

calc:

	for x=1 to len(a$)
		if mid$(a$,x)="/" or mid$(a$,x)="*" or mid$(a$,x)="-" or mid$(a$,x)="+"
			for i=1 to x-1
				a=a*10+val(mid$(a$,i))
			next i
			for i=x+1 to len(a$)
				b=b*10+val(mid$(a$,i))
			next i
			goto calc2
		endif
	next x

calc2:
	if mid$(a$,x)="/" then c=a/b
	if mid$(a$,x)="*" then c=a*b
	if mid$(a$,x)="+" then c=a+b
	if mid$(a$,x)="-" then c=a-b
	print c
	repeat
	sync
	until returnkey()=0
	suspend for key
goto restart

`functions
function returnnr()
	a$=""
	if hold=0
		if inkey$()="1" then a$="1" : hold=1
		if inkey$()="2" then a$="2" : hold=1
		if inkey$()="3" then a$="3" : hold=1
		if inkey$()="4" then a$="4" : hold=1
		if inkey$()="5" then a$="5" : hold=1
		if inkey$()="6" then a$="6" : hold=1
		if inkey$()="7" then a$="7" : hold=1
		if inkey$()="8" then a$="8" : hold=1
		if inkey$()="9" then a$="9" : hold=1
		if inkey$()="0" then a$="0" : hold=1
		if s=0
			if inkey$()="*" then a$="*" : hold=1 : s=1
			if inkey$()="-" then a$="-" : hold=1 : s=1
			if inkey$()="/" then a$="/" : hold=1 : s=1
			if inkey$()="+" then a$="+" : hold=1 : s=1
		endif
	endif
	if scancode()=0 then hold=0
endfunction a$