Qt Code: 
  1. void Calculator::calculation(QString &operation, QString &text_display)
  2. {
  3. 	QString a_string = "", b_string = "", result_string = "", temp_string = "";
  4. 	double a, b, result;
  5. 	int position, i, j;
  6.  
  7.  
  8. 		position = operation.indexOf("*", 0) ;
  9.  
  10. 		for( i = position - 1; i >= 0 ; i-- )
  11. 		{
  12. 			if( operation.at( i ) == '*' || operation.at( i ) == '/' || operation.at( i ) == '+' || operation.at( i ) == '-' )
  13. 				break;
  14. 			temp_string = a_string;
  15. 			a_string = operation.at( i ) + temp_string;
  16. 		}
  17.          ui.display->setText( a_string ); //displays a_string on QLineEdit
  18.  
  19. }
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Basically this function has to extract a number placed before '*' operator.
When operation = "3+56*35" a_string = "56" and it works correctly. But when operation="56*35" (without any operator before "56" - that is importanat) it multiplies extraced 56 three times and a_string = "565656". I've been thinking for a few hours about that and the problem still exists.

Thanks for help.