如何遍历一个函数一定次数？

Question

I have this function that takes the string values of '1' and adds a '0' to it.

The problem is that I want it to go through the function a set number of times. ie I want it to go 6 times so the number ends up being '1' '0' '1' '0' '1' '0' then using the join function to have them as one single value in an array

 alert(stringy()); //write a function that names stringy function stringy(size) { //create and empty array to hold new value var num = [] //push a the string value of 1 into array num.push('1') //loop through the array and if the variable equals 1 then push a 0 for (i = 0; i < num.length; i++) { if (num[i] == '1') { num.push('0') //if num has 0 in in it push 1 } else if (num[i] == '0') { num.push('1') } //numbers return two values in array but does not specify how many goes in. return num.join(); } //incomplete: only shows '1,0' in output one time. } 

Answer 1

You need a condition before returning, checking that the array size is equal to what is asked for:

if (num.length >= size) {
    return num.join();
}

The > is a safety to avoid infinite looping when size is less than 2. Don't forget to pass a size when you call the function.

Note that it is bad practice to add to an array while iterating over it: this can be confusing and the cause of undetected bugs. I seem to understand that you got this as a template in a course or something. If so, forget this way of working.

A better design for such a function is:

 function stringy(size){ return Array.from(Array(size), (_, i) => 1-(i%2)).join(''); } console.log(stringy(5)); console.log(stringy(6)); 

And, there is even a String#repeat function:

 function stringy(size){ return '10'.repeat(size/2+1).substr(0,size); } console.log(stringy(5)); console.log(stringy(6)); 

Answer 2

A couple problems:

You're not using the passed size in your loop. And you're returning inside the for, which returns after just one iteration.

I think this is closer to what you want;

function stringy(size){

    var num=[]
    num.push('1')
    for(i=0; i < size; i++){
        if(num[i]=='1'){
            num.push('0')
        } else if(num[i]=='0'){
        num.push('1')    }
    }
    return num.join();
}

You can also simplify things a bit which helps the readability:

function stringy(size){
    var num=[1]
    for(i=0; i < size; i++){
        num.push( num[i]==1 ? 0 : 1)
    }
    return num.join();
}
console.log(stringy(6))

Answer 3

function something(size) {
    var iterations = Math.floor(size / 2);
    var result = '';

    for (var index = 0; index < iterations; index++) {
        result += '10';
    }

    return result;
}

Answer 4

/**
 * Use modulo operator:
 * The modulo operator (%) returns the division remainder.
 * So:
 *      0/2 = 0
 *      1/2 = 1
 *      2/2 = 0
 *      3/2 = 1
 *      4/2 = 0
 * @param size int Array size.
 * @return string Joined array: "1,0,1,0,1,0,..."
 */
function stringy(size) {
    var num = [];

    for (var i = 0; i < size; i++) {
        num.push((i % 2 === 0) ? 1 : 0);
    }

    return num.join();
}