This calculator performs two digit task successfully but what do i need to alter it i want it to evaluate 3 digits

``````public class Calculator {

private long currentInput;          //current input
private long previousInput;         // previous input
private long result;            // result of calculation
private String lastOperator = "";  // keeps track of the last operator entered

/* New digit entered as integer value i - moves currentInput 1 decimal place to the left and adds i in "one's column" */
public void inDigit(long i) {
currentInput = (currentInput * 10) + i;
}

/* Operator entered  + - or *   */
public void inOperator(String op) {
previousInput = currentInput;      // save the new input as previous to get ready for next input
currentInput = 0;
lastOperator = op;                 // remember which operator was entered
}

/* Equals operation sets result to previousInput + - or * currentInput (depending on lastOperator) */
public void inEquals() {
if (lastOperator.equals("+")) {
result = previousInput + currentInput;
} else if (lastOperator.equals("-")) {
result = previousInput - currentInput;
} else if (lastOperator.equals("*"))  {
result = previousInput * currentInput;
}
lastOperator = "";       // reset last operator to "nothing"
}

/* Clear operation */
public void inClear() {
currentInput = 0;
previousInput = 0;
result = 0;
lastOperator = "";
}

/* returns the current result */
public String getResult() {
return Long.toString(result);  //converts int to String
}

/* returns the previous input value */
public String getPreviousInput() {
return Long.toString(previousInput);
}
/* returns the current input value */
public String getCurrentInput() {
return Long.toString(currentInput);
}``````

}

make the previousInput equal to the result, and then reuse it when you do another calculation

previousInput = 3
currentInput = 2
Sign = *
previousInput = result = 3*2 = 6

next operation

previousInput = 6
currentInput = 1
sign = -
previousInput = result = 6-1 = 5

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