Finding Prime Numbers between Two Numbers
<p>Am trying to find all prime numbers between two given numbers and sum the primes up.</p>

<p>I have this loop that does the prime number detection correctly. </p>

<p>However, for some reason I don't know how to sum all the primes.</p>

<pre><code>int a,b,i,j,sum=0;

do
{   cout &lt;&lt; "Enter a number: ";
    cin &gt;&gt; a;
    if (a &lt; 4 || a &gt; 1000000) 
    {   cout &lt;&lt; "Input must be between 4 and 1000000 inclusive." &lt;&lt; endl;
    }
}while (a &lt; 4 || a &gt; 1000000);

do
{   cout &lt;&lt; "Enter a second number: ";
    cin &gt;&gt; b;
    if (b &lt; 4 || b &gt; 1000000) 
    {   cout &lt;&lt; "Input must be between 4 and 1000000 inclusive." &lt;&lt; endl;
    }
}while (b &lt; 4 || b &gt; 1000000);

if (a &gt; b)
{   int hold;
    hold = b;
    b = a;
    a = hold;
}

cout &lt;&lt; "The prime numbers between " &lt;&lt; a &lt;&lt; " and " &lt;&lt; b &lt;&lt; " inclusive are: " &lt;&lt; endl;
//int sum;
for (i = a; i &lt;= b; i++)
{
 for (j = 2; j &lt;= i; j++) // Changed the &lt; to &lt;=, and got rid of semicolon
 {
    if (!(i%j)&amp;&amp;(i!=j)) break;
    if (j==i) 
    {
              cout &lt;&lt; i &lt;&lt; endl;
              sum += i;
              cout &lt;&lt; sum ;

    }
 }
}
</code></pre>

<p>The variable <code>sum</code> gives me rubbish results. </p>
