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Binary Search: A Method of Searching

Binary Search method is popular for searching a specific item in an ordered array (sorted). It can perform the search in minimum possible comparisons, but it needs the array to be sorted in any order.

Practically, it is used when the data is itself sorted initially or needs to be sorted for other activities also. This is because you don’t want to first sort the data and then use binary search, in that case use of linear search would be practical.

Binary Search Algorithm


  • The array to be AR[SIZE] having SIZE number of elements.

  • L is the index number of the lower element. We take it to be 0.

  • U is the index number of the upper (last) element. It will be (SIZE-1).

  • ITEM is the data that needs to be searched.

  • beg, last and mid are variables of type int(eger).

Here is the algorithm:

  1. LET beg = L AND last = U
  2. REPEAT STEPS 3 THROUGH 6 TILL beg<=last
  3. mid = ( (beg+last)/2)
  4. IF AR[mid] = ITEM THEN
           ITEM IS AT POSITION mid
           BREAK THE LOOP
  5. IF AR[mid] < ITEM THEN
           beg = mid+1
  6. IF AR[mid] > ITEM
           last = mid-1
  8. IF AR[mid] = ITEM THEN

Here is the example program:

  // example program in C++


  void main(void)
   int beg, last, mid, item, i;
   int ar[5];

   // sorted data needs to be input
   cout<<"enter sorted data:\n";
   for(i=0; i<5; i++)

   cout<<"enter search term:";

   // as per array

   // binary searching starts
      // calculate the middle
      // of the array section

      if (ar[mid]==item)
         cout<<item<<" found at index no. "<<mid;

        beg=mid+1;// should be beg=mid-1 for
        // data in descending order

        last=mid-1;// should be beg=mid+1 for
        // data in descending order
     // search end

     cout<<"\nSearch unsuccessfull!";


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