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  1. PO
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    <p>So, the first step when doing a recursive problem is to write out your iterative step, and the conditional at which you will stop recursing.</p> <p>Let's look at a function declaration:</p> <pre><code>float recursion(float n) { ... } </code></pre> <p>It sounds like your last iteration will be when:</p> <pre><code>(4. / n) - (4. / (n+2)) &lt; 0.0001 </code></pre> <p>And at each step, it looks like you want to add that delta to the total:</p> <pre><code>total += (4. / n) - (4. / (n+2)) </code></pre> <p>So let's start:</p> <pre><code>float recursion(int n) { // Calculate the delta at each step... const float delta = (4./n - 4./(n+2)); // If the delta is less than our tolerance, then we __don't__ recurse. // Depending on the requirements of your algorithm, you might return 0 here, // or delta as I have. if (delta &lt; 0.0001) return delta; // Otherwise, we should recurse. return delta + recursion(n+4); } </code></pre> <p>We could also implement this very easily as a loop instead of recursion. It's often helpful to do that to see the iteration process more clearly.</p> <pre><code>float iterative() { int n = 1; float total = 0; while (true) { // Calculate the delta at each step... const float delta = (4./n - 4./(n+2)); // If the delta is less than our tolerance, then we are done! if (delta &lt; 0.0001) return total + delta; // Otherwise, update the total and keep iterating. total += delta; n += 4; } } </code></pre> <p>Some things to note:</p> <ul> <li>In C, you need to be careful about integer division versus floating point division. In your code, you're fine because <code>n</code> is a float. In my code, I've changed <code>n</code> to be an integer, so I'm using <code>4.</code> instead of <code>4</code>, because that will be interpreted by the compiler as a <code>double float</code> (also known as a <code>double</code>), instead of as an integer.</li> <li>I'm iterating / recursing each time by 4. If you can't see why, then look at how much math is being done at each iteration.</li> <li>We only pass the denominator (which you named <code>n</code>) to each recursive function. Naming your variables better can help make this more clear.</li> </ul>
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    1. PORecursion code in series of 4/1 - 4/3 + 4/5
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    1. USBill Lynch
    1. USBill Lynch
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    1. COthanks for the help, for he had already done interactively, this problem started putting me to do recursive, and I'm a new student in the area of programming
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      1. USRicardo_Carvalho
 

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