TrivialBasic is a simplified implementation of the BASIC programming language
with the following features:

Statements:

LET variable=expression
INPUT variable
PRINT expression
PRINT "string"
GOTO linenumber
IF expression THEN statement
END

Every line must have a unique line number (integer)
and the last statement must be END.

Allowed variable names are single letters A-Z.
All variables are double precision floating point numbers.

Expressions follow C syntax, all operators that work
with floating point numbers are allowed, as well as
functions SQRT, SIN, COS, TAN, ASIN, ACOS, ATAN.
Comparison operators are also C-style: == != < > <= >=

To build, adjust 

Usage:
basic file.bas

The resulting executable is saved as "b.out" and
can be run again without recompilation (./b.out).