CODEWITHSUNDEEP
javascriptdebugging
user1758099
user1758099

Reputation: 11

New to Javascript. Can someone help me debug my program?

I'm trying to implement a binary search in javascript and I'm completely new at JS. I'm mostly used to the C++ syntax, so it's been a little difficult for me to break any habits that I have.

When I include this script in an html doc, it fails to exit the script if the array size is less than 1 and doesn't trigger the array order alert if I enter an unordered array. In addition, the program never seems to finish the while loop, so I don't know if there are any other problems.

Any help would be appreciated!

var size = parseInt(prompt("Enter the size of the array:"));

if(size < 1) {
    alert("ERROR: you entered an incorrect value for the array size!");
    return;
}

var arr = [size];
var input = parseInt(prompt("Enter the numbers in the array in increasing order,"
        + " separated by a space, and press enter:"));

arr = input.split(" ");

var checkOrder = function(array) {
    for(var i = 0; i < size-1; i++) {
        if(array[i] > array[i+1]) {
            return false;
        }
    }
    return true;
}

if(!checkOrder(arr)) {
    alert("The values entered for the array are not in increasing order!");
}

var search = parseInt(prompt("Enter a number to search for in the array: "));

var lp = 0; //left endpoint
var rp = size; //right endpoint
var mid = 0;
var counter = 0;
var found = false;

while(lp <= rp) {
    mid = Math.floor((lp + rp)/2);
    if(arr[mid] == search) {
        alert("Found value " + search + " at index " + mid);
        counter++;
        found = true;
        break;
    } else if(arr[mid] > search) {
        rp = mid + 1;
        counter++;
    } else {
        lp = mid;
        counter++;
    }
}

if(!found) {
    alert("The value " + search + "was not found in the array");
    alert("I wasted " + counter + " checks looking for a value that's not in the array!");
    return;
}

Upvotes: 1

Views: 115

Answers (2)

Leonid
Leonid

Reputation: 3171

Your input method is not right.
Putting array initialization issue aside, the line

var input = parseInt(prompt(".."))

gonna give you one single number.

You can actually skip prompting for array size

var input = prompt('Space separated numbers:')
var array = input.split(' ')
if (array.length == 0) {
    alert('._.'); return
}
for (var i = 0; i < array.length; i++)
    array[i] = parseInt(array[i])

Upvotes: 0

Greg Hewgill
Greg Hewgill

Reputation: 993423

var arr = [size];

The above code probably isn't doing what you want it to. This creates an array with one element, whose value is the value of size. You can create an array with a specific initial size by doing this:

var arr = new Array(size);

Upvotes: 3

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