ossp-pkg/js/src/perfect.js
// Some simple testing of new, eval and some string stuff.
// constructor -- expression array initialization
function ExprArray(n,v)
{
// Initializes n values to v coerced to a string.
for (var i = 0; i < n; i++) {
this[i] = "" + v;
}
}
// Print the perfect numbers up to n and the sum expression for n's divisors.
function perfect(n)
{
print("The perfect numbers up to " + n + " are:");
// We build sumOfDivisors[i] to hold a string expression for
// the sum of the divisors of i, excluding i itself.
var sumOfDivisors = new ExprArray(n+1,1);
for (var divisor = 2; divisor <= n; divisor++) {
for (var j = divisor + divisor; j <= n; j += divisor) {
sumOfDivisors[j] += " + " + divisor;
}
// At this point everything up to 'divisor' has its sumOfDivisors
// expression calculated, so we can determine whether it's perfect
// already by evaluating.
if (eval(sumOfDivisors[divisor]) == divisor) {
print("" + divisor + " = " + sumOfDivisors[divisor]);
}
}
print("That's all.");
}
print("\nA number is 'perfect' if it is equal to the sum of its")
print("divisors (excluding itself).\n");
perfect(500);
