Perform lexical operations that are implemented with a Finite Automata (or Finite State Machine).

Write a program in C++ to convert a character representation of a non-negative real number to a double value without using the string-to-double conversions, must do a character-by-character conversion. Use a separate method to do the actual conversion.

Note the ASCII characters for 0 through 9 are in order.

Do not use hardcoded numbers for ASCII values of digits or any other characters.

real ::= {0 | 1 | | 9}+ . {0 | 1 | | 9}* | {0 | 1 | | 9}* . {0 | 1 | | 9}+

Possible strings include 1., 3.14, .5. Note . must be present.

Something like this:

Token scan_real(char *line, int lookahead) /* scan a real number from input */

{

int pos = lookahead; /* remember start of number */

if (isdigit(line[lookahead])) { /* move from state 1 to state 2 */

while (isdigit(line[++lookahead])) /* stay in state 2 */

;

if (line[lookahead] = = .) { /* move to state 3 */

while (isdigit(line[++lookahead])) /* stay in state 3 */

;

strcpy(token.symbol, line + pos, lookahead pos); /* copy number to token */

}

else

printf(Syntax error: real number doesnt end with decimal point );

}

else if (line[lookahead] = = .) { /* move from state 1 to state 4 */

if (isdigit(line[++lookahead])) /* move from state 4 to state 5 */

same as state 3 above /* stay in state 5 */

else

printf(Syntax error: decimal point must be preceded or followed by digits);

}

else

printf(Syntax error: expected number, found %c , line[lookahead]);

}

0-9 start. 1) 0-9-23 . start 33 40-9.50-9 0-9 start. 1) 0-9-23 . start 33 40-9.50-9