Arduino Mega serial in and serial out to OLED

Projects Programming
16

if ( charJustRead == '4' ) // that's the one officer!
{
// arrest him!
}

My biggest concern would be getting the 'right' 4 out of the stream. I saw the dump you posted and there is a definite pattern with certain delimiter chars. After all, it is meant to be read and used. Have you gone through the data and defined for yourself what rules it works by?

A real simple data stream will always have the data in the same pattern but others get trickier. It looks to me like you should look of ".m" and then space digit space digit.

With text data you are reading ASCII values. Any text char in single quotes is the value.
char x = '0'; // now x == 48 == '0'
You can say space==32 and set up a var just for it or you can code ' ' and the code will be easier to read.
If you read a digit the value will be from '0' to '9', you subtract '0' from it and you have the value.

If you #include <ctypes.h>
http://www.nongnu.org/avr-libc/user-manual/group__ctype.html

Then you get these functions below which mostly return TRUE or FALSE.

<ctype.h>: Character Operations
Character classification routines

These functions perform character classification. They return true or false status depending whether the character passed to the function falls into the function's classification (i.e. isdigit() returns true if its argument is any value '0' though '9', inclusive). If the input is not an unsigned char value, all of this function return false.
int isalnum (int __c)
int isalpha (int __c)
int isascii (int __c)
int isblank (int __c)
int iscntrl (int __c)
int isdigit (int __c)
int isgraph (int __c)
int islower (int __c)
int isprint (int __c)
int ispunct (int __c)
int isspace (int __c)
int isupper (int __c)
int isxdigit (int __c)
Character convertion routines

This realization permits all possible values of integer argument. The toascii() function clears all highest bits. The tolower() and toupper() functions return an input argument as is, if it is not an unsigned char value.
int toascii (int __c)
int tolower (int __c)
int toupper (int __c)

I hope this helps.