Trying to make a function that prints an array range. I'm given the start, stop and step values. I keep getting an infinite loop

Question

I am trying to write a function that returns a list of integers from a 'start' value (inclusive) to a 'stop' value (exclusive) and am given the 'step' (or number to increment by...).

The function is supposed to be able to handle different amount of arguments passed in. I believe I have the function most of the way completed but I seem to be getting an infinite loop and am unsure why or how to proceed.

Here is the code I have written so far...

function range(start, stop, step) {
    if (arguments.length===1) {
        start = 0;
        stop = arguments[0];
        step = 1;
    } else if (arguments.length===2) {
        start = arguments[0];
        stop = arguments[1];
        step = 1;
    } else if (arguments.length===3) {
        start = arguments[0];
        stop = arguments[1];
        step = arguments[2];
    }
    // define result array
    let result = [];
    // create a for-loop
    for (start; start < stop; start + step) {
        result.push(start);
    }
    return result;
}

And here are some example calls and their expected outputs...

range(10); -> [0,1,2,3,4,5,6,7,8,9]
range(1,11); -> [1,2,3,4,5,6,7,8,9,10]
range(0,30,5); -> [0,5,10,15,20,25]
range(0,-10,-1); -> [0,-1,-2,-3,-4,-5,-6,-7,-8,-9]

The function is also supposed to be able to do negative ranges with negative 'step' values as well.

Could someone explain to me why I seem to be getting an infinite loop?

A for loop is made up of three expressions and a body: The expressions are (in order) initialization, test, and update. The update step should update something that is being used by the test step to determine whether the loop should keep going. start + step doesn't update anything, it just does a calculation and throws away the result. As @VLAZ said, you want to update start: start += step. — T.J. Crowder
– T.J. Crowder, Commented Dec 7, 2021 at 18:57

Saeed Shamloo · Accepted Answer · 2021-12-07 18:57:27Z

1

Because you don't change start value in your for loop. you have missed an =.

for (start; start < stop; start += step)

answered Dec 7, 2021 at 18:57

Saeed Shamloo

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1 Comment

DaShaman Over a year ago

Thank you for taking the time to look through and explain! I obviously need sleed!

lukas.j · Accepted Answer · 2021-12-07 19:49:07Z

Your code contains several mistake. For example you reassign values to the arguments, which one should never do. Then your for loop only works for stops which are greater than starts. And there is no error checking at all. Here is a self-explaining version which should work:

function range(start, stop, step) {
  for (let i = 0; i < arguments.length; i++) {
    if (!Number.isInteger(arguments[i])) {
      return [ 'Invalid arguments: all arguments must be of type Integer' ]
    }
  }
  let from = 0
  let to = 0
  let increment = 1
  if (arguments.length === 1) {
    to = arguments[0]
  } else if (arguments.length === 2) {
    [ from, to ] = arguments
  } else if (arguments.length === 3) {
    [ from, to, increment ] = arguments
  } else {
    return [ 'Invalid arguments: 0 or more than 3 arguments' ]
  }
  if (increment > 0 && from > to) {
    return [ 'Invalid arguments: step must be negative' ]
  } else if (increment < 0 && from < to) {
    return [ 'Invalid arguments: step must be positive' ]
  } else if (increment === 0) {
    return [ 'Invalid arguments: step cannot be 0' ]
  }
  let result = []
  if (increment > 0) {
    for (from; from < to; from += increment) {
      result.push(from)
    }
  } else {
    for (from; from > to; from += increment) {
      result.push(from)
    }
  }
  return result
}

console.log(range(10))             // [0,1,2,3,4,5,6,7,8,9]
console.log(range(1, 11))          // [1,2,3,4,5,6,7,8,9,10]
console.log(range(0, 30, 5))       // [0,5,10,15,20,25]
console.log(range(0, -10, -1))     // [0,-1,-2,-3,-4,-5,-6,-7,-8,-9]
console.log(range('0', 'abc'))     // Invalid arguments: all arguments must be of type Integer
console.log(range())               // Invalid arguments: 0 or more than 3 arguments
console.log(range(0, -10, 1))      // Invalid arguments: step must be negative
console.log(range(-20, -10, -1))   // Invalid arguments: step must be positive
console.log(range(0, 10, 0))       // Invalid arguments: step cannot be 0

A1exandr Belan · Accepted Answer · 2021-12-08 07:48:11Z

0

Another range solution:

const range = (start, stop, step) => {
  // manipulation with arguments
  const itemsCout = Math.ceil((stop - start) / step)
  return [...Array(itemsCout)].map((_value, index) => index*step+start )
};

console.log(range(1,10,2)); // [ 1, 3, 5, 7, 9 ]
console.log(range(0,30,5)); // [ 0, 5, 10, 15, 20, 25 ]
console.log(range(0,-10,-1)); // [ 0,-1,-2,-3,-4,-5,-6,-7,-8,-9 ]

answered Dec 8, 2021 at 7:48

A1exandr Belan

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