whileLoops.js

Question

Here's my line of code that I had trouble on.
// 1. Write a while loop to build a string of numbers from 0 to 4, 
//    separated by spaces, and store the string in the variable text.
print('1st Loop:');
text = '';
// Write 1st loop here:
let i = 0;
while( i <= 4) {
  text += i + ' ';
  i += 1;
}
print(text); // Should print 0 1 2 3 4.
// 2. Write a while loop to build a string of numbers from 1 to 5, 
//    separated by spaces, and store the string in the variable text.
print('2nd Loop:');
text = '';
// Write 2nd loop here:
let I = 1;
while ( I <= 5) {
 text += I + ' ';
  I += 1;
}
print(text); // Should print 1 2 3 4 5.
// 3. Write a while loop to build a string of numbers from 5 to 1, 
//    separated by spaces, and store the string in the variable text.
print('3rd Loop:');
text = '';
// Write 3rd loop here:
let i = 0;
while (i >= 1) {
  text += i + ' ';
  let i -= 1;
}
print(text); // Should print 5 4 3 2 1.
// 4. Write a while loop to build a string of numbers from 5 to 50--by 5's.
//    The numbers should be separated by spaces, and stored in the variable text.
print('4th Loop:');
text = '';
// Write 4th loop here:
print(text); // Should print 5 10 15 20 25 30 35 40 45 50.
// 5. BONUS CHALLENGE: Write a while loop that builds a string of random integers
// between 0 and 9. Stop building the string when the number 8 comes up.
// Be sure that 8 does print as the last character. The resulting string 
// will be a random length.
print('5th Loop:');
text = '';
// Write 5th loop here:
print(text); // Should print something like 4 7 2 9 8, or 9 0 8 or 8.
// Feel free to ignore this print function. It just formats the output a bit.
function print(text) {
  console.log(text);
  if (!text.endsWith(':')) {
    console.log('');
  }
I know the solution now, but I was very confused on why we couldn't use the let variable to define what ' i ' was. I only have come to a solution, because I looked at the solutions video, but I was just wondering if someone would care to explain to me what is going on if we define the ' i ' with the let variable.

Kristian Rosenqvist · Answer

You can only declare a variable once, unless it's part of a separate scope (like a for loop or a function). Once it has been declared to exist in a certain scope, you can reassign it or initialize it, but if you try to redeclare it in the same scope you get an error.
In your case you have declared i in the global scope before a while loop, and then you try to redeclare it later before a second while loop, which gives you an error.
For example, the following code would be acceptable:
```javascript
let i;
i=0;
while (condition1) {}
i=0
while (condition2) {}
```
This is actually what happens under the hood when you do something like:
```javascript
let i=0;
while (condition1) {}
i=0;
while (condition2) {}
```
Javascript automatically moves all variable declarations to the top of the scope like seen in the first code example.
Here's an example of a case where it would be acceptable to declare i twice. 
```javascript
let i=1;
function returnNumber() {
    let i =2;
    return i;
}
console.log(i + returnNumber());
//Output is: 12
```
The reason this works is becase i exists as a separate variable in the global scope and the function scope. If we had left out "let" in the function, we would have accessed and changed the global variable i instead.
I hope this was of some help. If you want to learn more about this you should read about Javascript variable scoping.

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adrian garcia

adrian garcia

whileLoops.js

1 Answer

Kristian Rosenqvist

Kristian Rosenqvist