16. The apparatus of claim 10 , wherein the control unit controls the display unit to display a pop-up window containing the calculation result close to the arithmetic expression.
10. An apparatus for performing calculations of a electronic device, comprising: a display unit displaying input characters in a character input window; and a control unit checking whether an arithmetic expression is present in the displayed input characters, calculating the arithmetic expression when the arithmetic expression is present in the displayed input characters, and controlling the display unit to display a result of the calculation.