title: Insert string after substring
body: <p>Maybe my title is weird :(
  <br>I have a problem here, I want to insert string into string.<br>
  First I input string that I want to insert, and input second string where the place where the previous stringis inserted<br>
  <br>
  Here is my code</p>
  
  <pre><code>string a,b;
  string str;
  
  cin &gt;&gt; a &gt;&gt; b;
  str.insert(b,a);
  </code></pre>
  
  <p><br>
  Here the example :<br></p>
  
  <pre><code>str = "ihaveadream";
  a = "simple";
  b = "ihavea";
  </code></pre>
  
  <p><br>
  Then the final result of str is:<br></p>
  
  <pre><code>str = "ihaveasimpledream";
  </code></pre>
  
  <p>In other words, the string <code>a</code> will be inserted after string <code>b</code><br>
  How can I do that? Thank you</p>