Thanks for the explanation 
Didnāt realize I couldnāt define xval3 in a case preceding the one in which I used it in a statement.
You should read up on variable scope in C/C++. It's important to understand that concept. Briefly, a variable that you create in a function or block is local to that function or block, and cannot be seen outside. A block is anything defined within curly braces - so in your case, since you defined xval3 within the curly braces of an if-statement, that variable cannot be seen outside of that if (not even in the else part of the if-else).
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