[error] Calculator

I've started testing a bit with cc and made a simple calculator program. However, everytime I try to do * it says calculator:18: attempt to perform arithmetic on local 'f' (a nil value)
Here's the code:

function add(x, y)
x = tonumber(x)
y = tonumber(y)
result = x+y
print ("Result: "..result)
end

function sub(p, q)
p = tonumber(p)
q = tonumber(q)
result2 = p-q
print ("Result: "..result2)
end

function abc(f, m)
f = tonumber(f)
m = tonumber(m)
result3 = f*m
print ("Result: "..result3)
end

function cba(k, l )
k = tonumber(k)
l = tonumber(l)
result4 = k/l
print ("Result: "..result4)
end

print "Calculator"

print "+, -, * or /"
input = io.read()

if input == "+" then

io.write "Enter first number: "
a = io.read()
io.write "Enter second number: "
b = io.read()
add(a, b )

elseif input == "-" then

io.write "Enter first number: "
c = io.read()
io.write "Enter second number: "
d = io.read()
sub(c, d)

elseif input == "*" then

io.write "Enter first number: "
e = io.read()
io.write "Enter second number: "
f = io.read()
abc(c,d)

elseif input == "/" then

io.write"Enter first number: "
g = io.read()
io.write "Enter second number: "
h = io.read()
cba(g, h)

else
print "Invalid action"
end

I know it isn't really compact but I'm not that good at coding so I just wanted it to be simple to understand.
(Can't get code tags around it right now but will do later)

we need code or we cannot help… all i can tell you from that error code is that there is an error on line 18. and you are trying to add something.

But I've checked it if it was exactly the same as the other functions and it is, the only difference is the *, perhaps it's not the right symbol?
Ps: sorry, forgot to paste the code in before posting

your problem is on line 56 you have

abc(c,d)

but above there you use the variables e and f

io.write "Enter first number: "
e = io.read()
io.write "Enter second number: "
f = io.read()

I actually got a different error than you…. odd… I got "test:18: attempt to perform arithmetic __mul on nil and nil"

on line 53 change

io.write "Enter first number: "
e = io.read()
io.write "Enter second number: "
f = io.read()
abc(c,d)

to

io.write "Enter first number: "
c = io.read()
io.write "Enter second number: "
d = io.read()
abc(c,d)

EDIT: Ninja'd :ph34r:/>

I really didn't expect it to be that simple…..
Thanks for helping so quick!
ps: you've probably got a different error because the las time I've tested it it wasn't in cc