This app shows how computer subtracts two numbers. The first two lines represent two numbers we are working on. The second two lines represent the conversion to adding by complement number method. The third two lines represent the reduced two numbers. You can put the results of the logic operations on the fourth two lines by clicking the digits. Logic operation for the reduced sum: 00->00, (01,10)->01, 11->10. If you click the digits according to the logic operation, you will have the value for the subtraction of two numbers eventually.