title: How to convert string to float in objective-c
body: <p>I have string and I want to convert into double value. I have written code but sometimes my program is being crashed.</p>
  
  <pre><code>double left_operand=[operand_1 doubleValue];
  </code></pre>
  
  <p>Here <code>operand_1</code> is NSString variable and i want to convert it into double value. Sometimes above code is crashing my program (automatically closed simulator)</p>
  
  <p>Is above code right?</p>