Question 373422 in Javascript Question posted in
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Javascript – using for loops to swap digits

using a for loop i have to write code to swap the 2nd and 3rd digit of a number given via user input in javascript.

for ( i = 0; i < entNum.length; i++) {
    if (i === 0) num2 = entNum[i];
    else if (i === entNum.length - 2) {
        newNum = newNum + num2;
        newNum = entNum[i] + newNum;
    }
    else newNum = newNum + entNum[i];
}
console.log("New number:" + newNum)

this is the code i was able to produce however this code swaps the 1st and 2nd digit in the number and i can’t seems to alter the code in the way to target the 2nd and 3rd digit nor do i 100% understand for loops and if statements. so a detailed explanation would be useful.

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4

Answers


  1. 0

    Usually you want to create functions for the things you make so you can reuse it. Here I’m converting your number into a string and then split it into an array, swap the digits and join back.

    function swap(val, x, y) {
    let arr = (val + "").split("");
    let tmp = arr[x];
    arr[x] = arr[y];
    arr[y] = tmp;
    return parseInt(arr.join(""));
}

console.log(swap(12345, 1, 2));

    If you really need a loop, then

    function swaps(input, x, y) {
    let arr = (input + "").split("");
    for (let index = 0; index < x.length; index++) {
        let tmp = arr[x[index]];
        arr[x[index]] = arr[y[index]];
        arr[y[index]] = tmp;
    }
    return parseInt(arr.join(""));
}

console.log(swaps(123456, [1], [2]));
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  2. 0

    You don’t even need a loop. You can do this with a string representation of the number.

    //make sure v1 is before b2
let str = "" + entNum;
let char1 = entNum.charAt(v1);
let char2 = entNum.charAt(v2);
str = str.substr(0,v1) + v2 + str.substring(v1 + 1, str.length) + v1;
entNum = parseInt(str);
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  3. 0

    Loop over the input string, concatenating each digit to the output string. Except if the index is 1 or 2, append the digit at the other index to swap them.

    let entNum = '123456';
let newNum = '';
for (let i = 0; i < entNum.length; i++) {
  let digit;
  if (i === 1) {
    digit = entNum[2];
  } else if (i == 2) {
    digit = entNum[1];
  } else {
    digit = entNum[i];
  }
  newNum += digit;
}
console.log("New number:" + newNum)
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  4. 0

    Function to swap consecutive values from starting position in a string using a loop:

    console.log(swapNumbers(`1234567`, 1));
console.log(swapNumbers(`1234567`, 4));

function swapNumbers(str, atPpos){
  const nrs = str.split(``);
  for (let i=0; i< nrs.length; i+=1) {
    if (i == atPpos) {
      [nrs[i], nrs[i+1]] = [nrs[i+1], nrs[i]];
      break;
    }
  }
  return nrs.join(``)
}
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