javascript - 为什么我的 javascript 显示值未建立？

Question

我正在尝试在数组中进行二分搜索，但即使我在提示输入中输入了数组中的数字，我的 javascript 也没有显示任何值

var array = [10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 100, 102, 105, 200, 250, 300, 320, 350];
var search = parseInt(prompt("enter what you search for"));
var first = 0,
  last = array.length - 1,
  position = 0,
  middle, flag = false;

while ((flag == false) && (first <= last)) {
  middle = ((first + last) / 2);
  if (array[middle] == search) {
    flag = true;
    position = middle;
  } else
  if (array[middle] > search)
    last = middle - 1;

  else
    first = middle + 1;
}
if (flag)
  document.write("</br>value founded in position  " + position);
else
  document.write("</br>value not founded ");

Answer 1

middle value calculation.

 middle = Math.round(first + ((last - first) / 2)); 

//你的代码..

var array =[10,20,30,40,50,60,70,80,90,95,100,102,105,200,250,300,320,350] ;
var search= 20; //parseInt(prompt ("enter what you search for"));

var first=0, last=array.length-1, 
position=0,
middle ,
flag=false;

while((flag==false) && (first <=last)) {
 middle = Math.round(first + ((last - first) / 2)); //((first+last)/2); low + (last - low)/2
 if (array[middle]==search){
     flag=true;
     position=middle ;
 }else if(array[middle]>search) {
     last=middle-1 ;
 }
 else {
    first= middle+1;
 }

}
if (flag) 
document.write ("</br>value founded in position  "+position);
else
document.write("</br>value not founded ");