Binary Search

1. int main() 
2. {
3.   int a[20] = {0};
4.   int n,
5. 
   
   i, j, temp;   int *beg,
6. 
   
   *end, *mid, target;
     printf(" enter the total integers you want to enter (make it less then 20):\n");
7.   scanf("%d", &n);
8.   if (n >= 20) return 0;   //  ouch!
9.   printf(" enter the integer array elements:\n" );
10.   for(i = 0; i < n; i++)
11.   {
12.     scanf("%d", &a[i]);
13.   }
14. // sort the loaded array, a  must for binary search!
15.   // you can apply qsort or  other algorithms here
16.   for(i = 0;  i < n-1; i++)
17.   { 
18.     for(j = 0; j < n-i-1; j++)
19.     {
20.       if (a[j+1] < a[j])
21.       {
22.         temp = a[j];
23.         a[j] = a[j+1];
24.         a[j+1] = temp;
25.       }
26.  }
27.  }
28. printf(" the sorted numbers  are:");
29.  for(i = 0; i < n; i++)
30.   {
31.  printf("%d ", a[i]);
32. 
    
33. 
    
      }
      // point to beginning and end of the array
34. 
    
      beg = &a[0];
      end = &a[n];  // use n = one element past the loaded array!
35.   printf("\n beg points to address %d and end to %d",beg, end);  // test
36.   // mid should point somewhere in the middle of these addresses
37.   mid = beg += n/2;
38.   printf("\n mid points to address %d", mid);  // test
39.   printf("\n enter the number to be searched:");
40.   scanf("%d",&target);
41.   // binary search, there is an AND in the middle of while()!!!
42. 
    
43. 
    
      while((beg <= end) && (*mid != target))
      {
44.     // is the target in lower or upper half?
45.   if (target < *mid)
46.   {
47.       end = mid - 1;     // new end
48.   n = n/2;
49.  mid = beg += n/2;  // new middle
50.     }
51.     else
52.     {
53.  beg = mid + 1;     // new beginning
54.   n = n/2;
55.   mid = beg += n/2;  // new middle     
56. }
57.   }
58.  // did you find the target?
59. 
    
60. 
    
      if (*mid == target)
      {
61.  printf("\n %d found!", target);
62.   }
63.   else
64.   {
65. printf("\n %d not found!", target);
66.  }
67.   getchar();  // trap enter
68.  getchar();  // wait
69.   return 0;
70. }
71.