Binary search to find the range in which the number lies
<p>I have an array</p>

<pre><code>Values array: 12 20 32 40 52
              ^  ^  ^  ^  ^
              0  1  2  3  4
</code></pre>

<p>on which I have to perform binary search to find the index of the range in which the number lies. For example:</p>

<ol>
<li>Given the number ->  19 (It lies between index 0 and 1), return 0</li>
<li>Given the number ->  22 (It lies between index 1 and 2), return 1</li>
<li>Given the number -> 40 (It lies between index 3 and 4), return 3</li>
</ol>

<p>I implemented the binary search in the following manner, and this comes to be correct for case 1, and 3 but incorrect if we search for case 2 or 52, 55 32, etc.</p>

<pre><code>#include &lt;iostream&gt;
using namespace std;

int findIndex(int values[], int number, unsigned first, unsigned last)
{
    unsigned midPoint;
    while(first&lt;last)
    {
        unsigned midPoint = (first+last)/2;
        if (number &lt;= values[midPoint])
            last = midPoint -1;
        else if (number &gt; values[midPoint])
            first = midPoint + 1;
    }
    return midPoint;
}


int main()
{
    int a[] = {12, 20, 32, 40, 52};
    unsigned i = findIndex(a, 55, 0, 4);
    cout &lt;&lt; i;
}
</code></pre>

<p>Use of additional variables such as <code>bool found</code> is not allowed.</p>
