How to best handle many accept cases

Question

For class I'm working on an interpreter, currently working on the scanner. Being a class that will be called many many times, I would like for it to be optimized for speed. In the scanner, to categorize an operator you have to compare the current token to the 6 or so operators. What method is best for speed, but for also for readability.

1. Many cases in an if statement
2. Loop through a char array of every operator and compare
3. Switch statement

These are the only cases I could think of. Which is best, or if you have a better approach please share. I implemented #2 because it takes up the least amount of lines of code.

Answer 1

Any sensible hand-written scanner is based on a switch statement. Note that if you return special characters directly to the parser as themselves, you can economize on case actions:

switch (ch) // the next incoming character
{
    case '+':
    case '-':
    case '*':
    case '/':
    case '%':
    // etc.
        return ch;
    case 'A':
    case 'B':
    // ...
    case 'Z':
    case 'a':
    case 'b':
    // ...
    case 'z':
        // start of an identifier: accumulate it, with a do/while loop,
        // save it somewhere, return IDENTIFIER
        return IDENTIFIER;
    case '0':
    case '1':
    // ...
    case '9':
        // start of a numeric literal: ...
        return NUMERIC_LITERAL;
    // etc. 
}