How can I not end the while loop?

• 0
  Hello, I'm doing a js assignment:
  
  

  Write a program that sequentially asks the user for a number using a prompt until he clicks Cancel. After clicking “Cancel”, the program displays the sum of the entered numbers using alert. If the user entered not a number (but, for example, a string), then this value is not added to the rest.

  
  
  Wrote code like this:
  

  let sum = 0;
   
  while (i = +prompt('Введите число: ')) {
      sum += i;
  };
  
  alert('Сумма: ' + sum);

  
  
  Everything seems to be fine, but how to make sure that the loop does not cancel when the user enters a line? You just need to skip it and when you need to display the sum of all numbers without the entered lines.

  JavaScript Anonymous, Jan 29, 2020

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4 Answers
• 0

  let sum = 0;
  
  let strNumber = 0;
  
  let number = 0;
  
  while (strNumber !== null) {
  
    strNumber = prompt("Введите число:", ""); // Получаем из prompt строку либо число в виде строки, если нажата отмена то вернёт null
  
    number = Number(strNumber); // Приводим строку к числу, если строка не может быть числом то вернёт NaN см. https://learn.javascript.ru/type-conversions
  
    sum += (!isNaN(number)) ? number : 0; // Использую isNaN потому что Number.isNaN не будет работать в IE у isNaN есть особености см (https://developer.mozilla.org/ru/docs/Web/JavaScript/Reference/Global_Objects/isNaN)
  
  }
  
  if(sum) {
  
    alert(sum);
  
  }

  Anonymous

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• 0
  Answer to the question:
  
  

  let sum = 0;
  
   
  
  while (i = prompt('Введите число: ')) {
  
      let j = parseInt(i, 10);
  
      if (Number.isNaN(j)) {
  
        continue;
  
      }
  
      sum += j;
  
  };
  
  
  
  alert('Сумма: ' + sum);

  
  
  
  
  In more detail, then your script crashed when the + prompt was applied if the user entered a letter.

  Anonymous

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• 0
  The prompt always contains a string. This string can be interpreted as a number, and in different ways, incl. as Roman notation: I, II, III, IV, V, VI, VII, VIII, IX, X, ...
  
  
  
  I don’t remember offhand what the prompt returns when I click Cancel. Read the documentation.
  
  But you certainly don't need to convert the return value to a number right away. First you need to check for cancellation, and if so, then leave the cycle.

  Anonymous

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• 0

  const arr = [];
  
  
  
  function setintPromt() {
  
    let num = prompt('Введите число: ', '');
  
    if (num === null) {
  
      let result = arr.length ? eval(arr.join('+')) : 0;
  
      return alert(result);
  
    }
  
    if (+num) {
  
      arr.push(num);
  
    }
  
    setintPromt();
  
  }
  
  setintPromt();

  Anonymous

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