How to make a simple touch calculator using Arduino & Nintendo DS Touch Screen?

I have an Arduino Uno, a lcd & a Nintendo DS Touch Screen. I'm able to make a touchscreen keypad using nintendo ds but i want touch input be stored somewhere unless user presses an operator(+,-,/,*) between two single digit numbers followed by the "=" key like "2+3=". And on pressing the "=" key the result should be displayed on lcd if the inputs are valid. I just want basic 4 operation for now i.e add,subtract,multiply and divide. How to do it.....i want programming help.

Thanxx in advance.

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