Setting Up A For Loop For An Encryption Scheme

As I stated before I am trying to make a specific for loop for an encryption machine (a toy machine, not one that is secure from the NSA). When I press the encrypt button, I need t

Solution 1:

Here's an interpretation of what I think you're trying to do:

functionencrypt(num) {
    var sum = 0, str, i, result, index;
    var chars = "abcdefghijklmnop";
    var charBase = "0".charCodeAt(0);
    for (i = 0; i < 5; i++) {
        // ((2 * i) + 3) goes 3,5,7,9,11// ((i * 10) + 10) goes 10,20,30,40,50
        sum += (num * ((2 * i) + 3)) + ((i * 10) + 10);        
    }
    // convert num to string to get digits
    str = sum + "";
    result = "";
    for (i = 0; i < str.length; i++) {
        // get offset from "0" and add 3 for the cipher
        index = str.charCodeAt(i) - charBase + 3;
        // convert that index to a character
        result += chars.charAt(index);
    }
    return result;
}

It takes a number as an argument and it returns a string.

Working demo: http://jsfiddle.net/jfriend00/UW245/