Three Ways to do Sequential Search

Setup: We have an array of strings called 'List', indexed from 0 to 1000.  One
thousand strings are stored in 'List' in slots 1 through 1000.  List[0] is
unused.  The strings are in no particular order within the array.

Method One: For Loop Search for a string stored in the variable 'target'

int location = -1 ;
For (int i=1; i<=1000; i++)
{
  if   List[i] == target 
  then location = i ;
}

Advantage: very simple to code

Disadvantage: takes more time than it needs to - does not stop searching when
target is found.


Method Two: While-Loop Search for 'target'

int i = 0;
bool found = false ;

While (i<=999 && !found)
{
  i = i+1;
  if   List[i] == target 
  then found = true ;
}
 
Advantage: Assuming target is equally likely to be in any of the 1000 slots,
this checks only half as many slots as Method One, on average.

Disadvantage: Each time through the loop there's an extra check to see if
'found' is still false - so each "probe" requires one more test than Method
One.


Method Three: Sentinel Search

int i=1000; 
bool found=false;
List[0]= target ;

While (List[i] != target) i-- ;

Advantage: Checks only half the slots on average - like Method Two.  Also does
only one test per iteration of the loop.

Disadvantage: It's O(n) - like Method One and Method Two