Question

I need to a function to convert an integer to the equivalent alpha ordered list index. For example:

1 = a
2 = b
.
.
.
26 = z
27 = aa
28 = ab
.
.
etc.

Currently I have the following which almost works but there’s a small logic error somewhere that makes it not quite get it right (it goes ax, ay, bz, ba, bb, bc…):

function intToAlpha( int ) {

    var asciiStart = 97,
        alphaMax = 26,
        asciiCode,
        char,
        alpha = '',
        place,
        num,
        i;

    for ( i = 0; Math.pow(alphaMax, i) < int; i++ ) {

        place = Math.pow(alphaMax, i);        
        num = Math.floor( ( int / place ) % alphaMax);
        asciiCode = ( num == 0 ? alphaMax : num ) + asciiStart - 1;
        char = String.fromCharCode(asciiCode);
        alpha = char + alpha;

    }

    return alpha;
}

for (i = 1; i < 300; i++) {
    console.log( i + ': ' + intToAlpha(i) );
}

Answer 1

This function is used in NVu/Kompozer/SeaMonkey Composer, with a small tweak to generate lower case directly:

function ConvertArabicToLetters(num)
{
  var letters = "";
  while (num > 0) {
    num--;
    letters = String.fromCharCode(97 + (num % 26)) + letters;
    num = Math.floor(num / 26);
  }
  return letters;
}