CODEWITHSUNDEEP
javascriptarraysfunction
T.M.
T.M.

Reputation: 29

Why is function producing wrong solution

   <script>
    function range (start , end ) {
      var list =[]
      for (var count = start ; count <= end ; count++)
        list.push(count);
      return list
    }

    function sum ( nums ) {
      var total = 0;
      for ( var count = 0 ; count <= nums.length ; count++ )
        total = total + nums[count];
      return total;
    }

    console.log(range(1 , 10))
    console.log(sum(range(1 ,10)))
    </script>

When I run this, the output from my sum function will be NaN. I know the solution is to remove the = from the sum function however I do not understand how this solves the problem.

Upvotes: 1

Views: 54

Answers (2)

TheRealMrCrowley
TheRealMrCrowley

Reputation: 976

when you <= that means you are including the end number. all arrays are 0 indexed, meaning the first item is at index 0

for an array of 10 items, this means the the last index is 9

also for incrementing an existing number you can use +=

function range (start , end ) {
  var list =[]

  //here you want INCLUSIVE because you are starting 
  //at VALUE 1 and ending at VALUE 10
  for (var count = start ; count <= end ; count++)
    list.push(count);
  return list
}

function sum ( nums ) {
  var total = 0;

  //here you want EXCLUSIVE because you are starting
  //at INDEX 0 and ending at INDEX 9
  for ( var count = 0 ; count < nums.length ; count++ )
    total += nums[count];
  return total;
}

console.log(sum(range(1,10)))

Upvotes: 1

janos
janos

Reputation: 124648

You are iterating beyond the bounds of the nums array. As such, in the last iteration of the loop you effectively execute total = total + undefined, the result of which is NaN. Try for example in a JavaScript console, n + undefined results in NaN, where n is any number.

Change the loop condition to count < nums.length instead of <=:

  for ( var count = 0 ; count < nums.length ; count++ )
    total = total + nums[count];

Upvotes: 5

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