CS130 - 4/13/11

1. No news :(
2. Cascading if-elses; to do one of a number of things
3. Example: they type 3, +, 1, -, 2, = (state of the display, state of the program/computation)
4. What to do with operators (+, -, *, /, =)
   1. Update total using current input and previous operator
   2. display new total
   3. set previous operator to what they just typed
5. Complications
   1. Initialization; what about the *first* operator?
   2. What if they type 3, +, 1, =, -, 2, =??
6. Ugly code/beautiful code -- for +, and -

       int PLUS=0;
       int MINUS=1;
       int EQUALS=2;
       int state=PLUS; // first operator is by default +
   
       void plusProto() {
           String s = inTF.getText();
           int currentInput = Integer.parseInt(s);
   
           // now apply the *previous* operator with the current input
           if (state == PLUS) {
               total = total + currentInput;
           }
           else if (state == MINUS) {
               total = total - currentInput;
           }
           else if (state == EQUALS) {
           }
           else {
               System.out.println("oops, *not* equal, plus or minus??");
           }
   
           state = PLUS;
           inTF.setText(""+total);
           inTF.requestFocus();
           inTF.selectAll();
       }
   
       void minusProto() {
           String s = inTF.getText();
           int currentInput = Integer.parseInt(s);
   
           // now apply the *previous* operator with the current input
           if (state == PLUS) {
               total = total + currentInput;
           }
           else if (state == MINUS) {
               total = total - currentInput;
           }
           else if (state == EQUALS) {
           }
           else {
               System.out.println("oops, *not* equal, plus or minus??");
           }
   
           state = MINUS;
           inTF.setText(""+total);
           inTF.requestFocus();
           inTF.selectAll();
       }

   What's wrong with this? Too long! Plus, the only difference is the state = PLUS and state = MINUS. So...

       int currentInput;
       int PLUS=0;
       int MINUS=1;
       int EQUALS=2;
       int state=PLUS; // first operator is by default +
   
       void setCurrentInput() {
           String s = inTF.getText();
           currentInput = Integer.parseInt(s);
       }
   
       void plusProto() {
           setCurrentInput();
           updateTotal();
           displayTotal();
           state = PLUS;
       }
   
       void minusProto() {
           setCurrentInput();
           updateTotal();
           displayTotal();
           state = MINUS;
       }
   
       void updateTotal() {
           // apply the *previous* operator with the current input
           if (state == PLUS) {
               total = total + currentInput;
           }
           else if (state == MINUS) {
               total = total - currentInput;
           }
           else if (state == EQUALS) {
           }
           else {
               System.out.println("oops, *not* equal, plus or minus??");
           }
       }
   
       void displayTotal() {
           inTF.setText(""+total);
           inTF.requestFocus();
           inTF.selectAll();
       }

   Which is quite a bit better... but... minusProto and plusProto are all the same code but one line, so...

       int PLUS=0;
       int MINUS=1;
       int EQUALS=2;
   
       int state=PLUS; // first operator is by default +
       int currentInput;
   
       void setCurrentInput() {
           String s = inTF.getText();
           currentInput = Integer.parseInt(s);
       }
   
       void plus() {
           update();
           state = PLUS;
       }
   
       void minus() {
          update();
          state = MINUS;
       }
   
       void update() {
           setCurrentInput();
           updateTotal();
           displayTotal();
       }
   
       void updateTotal() {
           // apply the *previous* operator with the current input
           if (state == PLUS) {
               total = total + currentInput;
           }
           else if (state == MINUS) {
               total = total - currentInput;
           }
           else if (state == EQUALS) {
           }
           else {
               System.out.println("oops, *not* equal, plus or minus??");
           }
       }
   
       void displayTotal() {
           inTF.setText(""+total);
           inTF.requestFocus();
           inTF.selectAll();
       }