About the binary lookup algorithm

At the end of February, the end of the spring to the warm, bright days, huifeng genial, sometimes really want to take the kite before, rushed out to experience a field run of joy. But also just think about it, more and more house I always can not leave the hands of the notebook computer.
Also do not know is the cause of the temperature rise or chunkun suddenly top of the reason, looked at a few days of the binary search algorithm only to understand it.
The binary lookup algorithm is a more efficient and concise algorithm than a sequential lookup, with a lookup length of up to ㏒2n+1 (the depth of the decision tree), and an average lookup length of ㏒2 (n+1)-1, but it has a big drawback that it is necessary to require the lookup sequence to store ordered tables sequentially.
Each of these algorithms can be represented by iteration and recursion, and I will use the C + + to represent the following.
Iterative form of C + +:

#include <stdio.h>
int find (int a[],int x,int low,int High)
{
    int mid;
    if (low>high)           //if ...  .   else ....  Error!!!
    return-1;
 while (Low<=high)
 {
     mid= (Low+high)/2;
    if (a[mid]==x)
    return mid;
    else if (a[mid]>x) high
     = Mid-1;

    else if (a[mid]<x) Low
     = mid + 1;
 }
}
int main ()
{
int a[20]={2,3,6,7,12,18,19,21,25,28,30,33,37,39,42,45,47,49,50,51};
int x,i;
printf ("Existing number is: \ n");
for (i=0;i<20;i++)
printf ("%d", A[i]);
printf ("\ n Please enter the number to look for:");
scanf ("%d", &x);
if ((I=find (a,x,0,19)) >=0)
printf ("%d is the number of%d \ n", x,i+1);
else 
printf ("%d\n not Found", x);
 return 0;
}

In the IF program, why should I add an inexplicable comment--if...else ... error. Because I wanted to use this structure before, but later found that I made a low-level error, our goal is to continue to cycle in the sub-program to change the upper and lower limits, to divide and conquer the algorithm, and if ... else ... It's just a judgment run, of course, not the same as our requirements.

A/C + + recursive form:

#include <stdio.h>
int find (int a[],int x,int low,int high)
{int mid;
 if (Low>high)
 return-1;
 Mid= (Low+high)/2;
return mid;
 if (a[mid]>x)
 return find (a,x,low,mid-1);
 return find (A,x,mid+1,high);
}
int main ()
{
int a[20]={2,3,6,7,12,18,19,21,25,28,30,33,37,39,42,45,47,49,50,51};
int x,i;
printf ("Existing number is: \ n");
for (i=0;i<20;i++)
printf ("%d", A[i]);
printf ("\ n Please enter the number to look for:");
scanf ("%d", &x);
if ((I=find (a,x,0,19)) >=0)
printf ("%d is the number of%d \ n", x,i+1);
else 
printf ("%d\n not Found", x);
 return 0;
}

The great recursive algorithm, but we have changed the data is easily thrown to the program itself, although to consume memory stack space, but the algorithm is relatively simple.