+ - * / two ints and output the result?? But how???

j_o_k_e_r · Joined: 10 Dec 2007 Posts: 3

Hi,

I'm quite new to the compiler and that is why if possible, I need a very quick and explanatory response to solve an urgent, but of course for some gurus a very silly problem. I need to program a 16F877A to take two numbers from the computer and make arithmetic operations (+ * / -) as if it is a calculator and output the result to the computer. More detaily, I will give two 1 byte (or 2 byte) integers and an operator (like: 3+4) from the keyboard and I want to get the result. I tried to use getc() and putc() for this purpose, and also I tried to assign the first and the third element as byte, char, int, etc. but nevertheless I couldn't get the result of such a silly operation. For example somehow I get 'e' for the result of 2+3 (decimal byte value of 2 is 50 and 3 is 51 and e is 101, definetly correct 50+51=101 but I want just 5 nothing more!) What kind of commands I should use to take expression (getc() or something else), what types of variables should I assign them (int, byte, char or what) and how should I output the result (is it putc() or what it should be)??? Please help me!

Thanks a lot.
Kind regards.

Foppie · Joined: 16 Sep 2005 Posts: 138 Location: The Netherlands

first thing I have to say is that int, byte and char are the same in CCS. They are all unsigned 8 bits variables.

To answer your question of how to do it:
You could read in the integers as you are doing now, and then substract '0' of those integers.

something like this:

j_o_k_e_r · Joined: 10 Dec 2007 Posts: 3

Foppie, thanks a lot for your interest, but the code doesn't work. Could you explain what might be the reason or what else should I do? (Meanwhile, what is the meaning of subtracting '0')

Foppie · Joined: 16 Sep 2005 Posts: 138 Location: The Netherlands

Substracting '0' is the same as substracting 48. So if a '2' is received as character, 50 is received as integer and then when '0' is substracted, you will get the integer value (and not the ascii value) in your variable.

I don't know why the code isn't working. Can you maybe describe what the error is that occures?
I know that the code will give results that you might think of as errors when overflows occur. You must remember that an int8 only can hold values between 0 and 255.

I hope this helps.

j_o_k_e_r · Joined: 10 Dec 2007 Posts: 3

I could finally find some way to handle the problem. Thanks foppie for your help. Kind regards.