Error: stray '\' in program //can someone take a look at this and tell me what I'm missing. I'm assuming I have a '\' in there that I shouldnt?

To add to what Richard has said, you should expect to get syntax errors every day, probably many times a day while you are coding - we all do regardless of how much experience we have! Sometimes, we misspell a variable, or a keyword; sometimes we forget to close a string or a code block. Sometimes the cat walks over your keyboard and types something really weird. Sometimes we just forget how many parameters a method call needs.

We all make mistakes.

And because we all do it, we all have to fix syntax errors - and it's a lot quicker to learn how and fix them yourself than to wait for someone else to fix them for you! So invest a little time in learning how to read error messages, and how to interpret your code as written in the light of what the compiler is telling you is wrong - it really is trying to be helpful!

So read this: How to Write Code to Solve a Problem, A Beginner's Guide Part 2: Syntax Errors[^] - it should help you next time you get a compilation error!

I realize you have already solved your issue but I wanted to point something out to you. In the C language a single string can span multiple line. You have to start and end each substring with a quote and there can be no commas between substrings. In your case you have this monstrosity of a string :

"{\"state"\:{\"reported"\:{\"co2"\:\" %d "\, \"temperature"\:\" %f "\, \"humidity"\:\" %f" \, \"pressure"\ :\" %f "\, \"battery"\ :\" %d" \, \"name"\ :\" co2-sensor" \, \"timestamp"\ : \" %d" \, \"ttl"\: \" %d " \ }}}"

If I were you, I would split it into substrings with each label and value on a line. This would make it much easier to see the cause of the problem you had. Here is a start for the first few items :

"{"
    "\"state"\:"
    "{"
        "\"reported"\:"
        "{"
             "\"co2"\:\" %d "
             "\, \"temperature"\:\" %f "
             // more items here - comments can also be at the ends of lines
        "}"
    "}"
"}"

and so on... This is all one string and the newline characters are not included in it. I am not sure I did that correctly because commas and colons do not need to be escaped with backslash, only quotes and other special characters do. When each item is separated I think it is much easier to see the problems.

cout << R"("<- no need for escape ->"<-can even hit new line just watch
" see i hit new line and bingo presto no problemo special characters all over the place w/o escape ->' ->")";