WinForm (iv)--Simple calculator production

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Code area:

usingSystem;usingSystem.Collections.Generic;usingSystem.ComponentModel;usingSystem.Data;usingSystem.Drawing;usingSystem.Linq;usingSystem.Text;usingSystem.Threading.Tasks;usingSystem.Windows.Forms;namespacewindowsformsapplication2{ Public Partial classForm1:form {//store Last click on what button, 0 means nothing to click, 1 for the number of clicks on the button, 2 for the operator clicked        Private intPrev =0; //intermediate results for storage calculations        Private decimalZJ =0; //record what operator was last pressed        Private stringPREVYSF ="+";  PublicForm1 () {InitializeComponent (); }        //number Key button        Private voidButton8_click (Objectsender, EventArgs e) {            //Convert an event source to a buttonButton btn = Sender asButton; //replace (if the text box below contains 0 or the last time you clicked the operator)            if(prev = =2|| Txtbottom. Text = ="0") {Txtbottom. Text=btn.            Text; }            //Append (if the contents of the text box below are not 0 and the last time there is no click operator)            Else{Txtbottom. Text+=btn.            Text; }            //Click the number buttonPrev =1; }        //operator Buttons        Private voidButton17_click (Objectsender, EventArgs e) {Button btn= Sender asButton; //last hit a number            if(prev = =1) {txttop. Text+ = Txtbottom. Text +btn.                Text; Switch(PREVYSF) { Case "+": ZJ= ZJ +Convert.todecimal (Txtbottom.                        Text);  Break;  Case "-": ZJ= ZJ-Convert.todecimal (Txtbottom.                        Text);  Break;  Case "*": ZJ= ZJ *Convert.todecimal (Txtbottom.                        Text);  Break;  Case "/": ZJ= ZJ/Convert.todecimal (Txtbottom.                        Text);  Break; } txtbottom. Text=ZJ.             ToString (); }            //the operator was last pressed            Else            {                strings =Txttop.                Text; S= S.substring (0, S.length-1); S= S +btn.                Text; Txttop. Text=s; }            //Click the operatorPrev =2; //Log the operatorPREVYSF =btn.                  Text; }        //Clear 0 Button        Private voidButton19_click (Objectsender, EventArgs e) {Txttop. Text=""; Txtbottom. Text="0"; Prev=0; ZJ=0; PREVYSF="+"; }        Private voidButton20_click (Objectsender, EventArgs e) {Txtbottom. Text="0"; }        //equal sign button        Private voidButton4_Click (Objectsender, EventArgs e) {Button btn= Sender asButton; Txttop. Text+ = Txtbottom. Text +btn.            Text; Switch(PREVYSF) { Case "+": ZJ= ZJ +Convert.todecimal (Txtbottom.                    Text);  Break;  Case "-": ZJ= ZJ-Convert.todecimal (Txtbottom.                    Text);  Break;  Case "*": ZJ= ZJ *Convert.todecimal (Txtbottom.                    Text);  Break;  Case "/": ZJ= ZJ/Convert.todecimal (Txtbottom.                    Text);  Break; } txtbottom. Text=ZJ.            ToString (); Txttop. Text=""; ZJ=0; }        //Point        Private voidButton3_Click (Objectsender, EventArgs e) {Txtbottom. Text+="."; }    }}

WinForm (iv)--Simple calculator production