VAL function

appendix/basic_commands.tex

@@ -2907,7 +2907,49 @@ \subsection{USR}
 
 \subsection{VAL}
 
-<TODO>
+The {\ttfamily VAL} function returns a numeric value representing the characters in a string argument.  Often a string 
+variable is passed to the function, but a literal string is also valid (eg. "  -540.15 "). Blank characters ("spaces") 
+in the string are ignored.  If the first non-blank character of the string is not a plus sign (+), minus sign (-), 
+dollar sign (\$), percentage sign (\%) or a digit the conversion ends with a value of zero (0).  These initial special 
+characters signify the type of number to follow - Positive (+); Negative (-); Hexadecimal (\$), which then validates 
+the letters A,B,C,D,E \& F; Binary Literal (\%) eg. "010101"; and 
+Numbers (0123456789).  Subsequent valid characters are additional digits (or the first decimal 
+point or E/e for Exponent).  The function ends at the end of the string, or the next non-digit character for that numberic 
+type and returns the converted result.  Subsequent digits after any non-valid characters are disregarded. 
+Other mathematical terms and arithmetic operations are ignored.\\
+
+The valid range of possible numbers is from -1e+38 to 1e+38. Outside of this range the error "?OVERFLOW ERROR IN <line>" 
+is shown and the program stops.  When the argument isn't a string, the error "?TYPE MISMATCH ERROR IN <line>" would 
+result and stop the program.  When the argument is absent, the error "?SYNTAX ERROR IN <line>" is returned and stops 
+the program.\\
+
+\codeblock{
+	10 READ A\$\\
+	20 DATA "  - 120 . 64  "\\
+	30 PRINT VAL(A\$)\\
+RUN\\
+-120.64\\
+}
+
+Examples:\\
+
+Leading letters are invalid, but don't cause an error.\newline 
+\codeblock{
+PRINT VAL("ABC 123")\\
+0\\
+}
+
+The binary literal string is converted to decimal number.\newline
+\codeblock{
+PRINT VAL("\%010101")\\
+21\\
+}
+
+The exponential notation string is returned as a simplified number.\newline
+\codeblock{
+PRINT VAL("+352 .25 E-3  Units")\\
+0.35225\\
+}
 
 \subsection{VPEEK}