// isEmail (STRING s)
// 
// Email address must be of form a@b.c ... in other words:
// * there must be at least one character before the @
// * there must be at least one character before and after the .
// * the characters @ and . are both required
//

function isEmail (s)
{
   if (isEmpty(s)) return false;
   
    // is s whitespace?
    if (isWhitespace(s)) return false;
    
    // there must be >= 1 character before @, so we
    // start looking at character position 1 
    // (i.e. second character)
    var i = 1;
    var sLength = s.length;

    // look for @
    while ((i < sLength) && (s.charAt(i) != "@"))
    { i++
    }

    if ((i >= sLength) || (s.charAt(i) != "@")) return false;
    else i += 2;

    // look for .
    while ((i < sLength) && (s.charAt(i) != "."))
    { i++
    }

    // there must be at least one character after the .
    if ((i >= sLength - 1) || (s.charAt(i) != ".")) return false;
    else return true;
}

// Check whether string s is empty.
function isEmpty(s)
{   
	return ((s == null) || (s.length == 0));
}


// whitespace characters
var whitespace = " \t\n\r";

// Returns true if string s is empty or 
// whitespace characters only.
function isWhitespace (s)
{   
	var i;

    // Is s empty?
    if (isEmpty(s)) return true;

    // Search through string's characters one by one
    // until we find a non-whitespace character.
    // When we do, return false; if we don't, return true.

    for (i = 0; i < s.length; i++)
    {   
		// Check that current character isn't whitespace.
		var c = s.charAt(i);
	
		if (whitespace.indexOf(c) == -1) return false;
    }

    // All characters are whitespace.
    return true;
}

var numeric = "1234567890-."
function isNumeric (s)
{
    for (i = 0; i < s.length; i++)
    {   
		// Check that current character is numeric.
		var c = s.charAt(i);
	
		if (numeric.indexOf(c) == -1) return false;
    }
	return true;
}