Folks have asked numerous times for a code snippet of a binary search of an array. Here is heavily commented code with a few test printf() included to give you a picture of what is going on.

# Binary Search of an Integer Array

```
// binary search of an integer array, this search is efficient for large arrays
// tested with PellesC vegaseat 24jan2005
#include <stdio.h>
int main()
{
int a[20] = {0};
int n, i, j, temp;
int *beg, *end, *mid, target;
printf(" enter the total integers you want to enter (make it less then 20):\n");
scanf("%d", &n);
if (n >= 20) return 0; // ouch!
printf(" enter the integer array elements:\n" );
for(i = 0; i < n; i++)
{
scanf("%d", &a[i]);
}
// sort the loaded array, a must for binary search!
// you can apply qsort or other algorithms here
for(i = 0; i < n-1; i++)
{
for(j = 0; j < n-i-1; j++)
{
if (a[j+1] < a[j])
{
temp = a[j];
a[j] = a[j+1];
a[j+1] = temp;
}
}
}
printf(" the sorted numbers are:");
for(i = 0; i < n; i++)
{
printf("%d ", a[i]);
}
// point to beginning and end of the array
beg = &a[0];
end = &a[n]; // use n = one element past the loaded array!
printf("\n beg points to address %d and end to %d",beg, end); // test
// mid should point somewhere in the middle of these addresses
mid = beg += n/2;
printf("\n mid points to address %d", mid); // test
printf("\n enter the number to be searched:");
scanf("%d",&target);
// binary search, there is an AND in the middle of while()!!!
while((beg <= end) && (*mid != target))
{
// is the target in lower or upper half?
if (target < *mid)
{
end = mid - 1; // new end
n = n/2;
mid = beg += n/2; // new middle
}
else
{
beg = mid + 1; // new beginning
n = n/2;
mid = beg += n/2; // new middle
}
}
// did you find the target?
if (*mid == target)
{
printf("\n %d found!", target);
}
else
{
printf("\n %d not found!", target);
}
getchar(); // trap enter
getchar(); // wait
return 0;
}
```

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