Java – the calculator does not handle two operator equations
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Java
I am developing a calculator application and all functions have been turned off The only problem is that when I enter an equation that contains two arithmetic operators, it breaks down For example, if you enter "2 √ 9", it will return to 3. If you enter "√ 92", it will be forced to close and "invalid double √ 9" will be displayed Please help.
ScientificCalculator. java
String prevAnswer = "";
TextView formulascreen;
TextView resultscreen;
String formuladisplay = "";
String resultdisplay = "";
String result = "";
String operator;
DecimalFormat res = new DecimalFormat("#,###,###.######");
@Nullable
@Override
public View onCreateView(LayoutInflater inflater,@Nullable ViewGroup container,@Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.scientific_calculator,container,false);
formulascreen = (TextView) view.findViewById(R.id.formulaTextView);
updateformuladisplay();
resultscreen = (TextView) view.findViewById(R.id.resultTextView);
updateresultdisplay();
view.findViewById(R.id.btn0).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickNumber(v);
}
});
view.findViewById(R.id.btn1).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickNumber(v);
}
});
view.findViewById(R.id.btn2).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickNumber(v);
}
});
view.findViewById(R.id.btn3).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickNumber(v);
}
});
view.findViewById(R.id.btn4).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickNumber(v);
}
});
view.findViewById(R.id.btn5).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickNumber(v);
}
});
view.findViewById(R.id.btn6).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickNumber(v);
}
});
view.findViewById(R.id.btn7).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickNumber(v);
}
});
view.findViewById(R.id.btn8).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickNumber(v);
}
});
view.findViewById(R.id.btn9).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickNumber(v);
}
});
view.findViewById(R.id.btnSqrt).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClicksqrt(v);
}
});
view.findViewById(R.id.btnClear).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickClear(v);
}
});
view.findViewById(R.id.btnDel).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickDel(v);
}
});
view.findViewById(R.id.btnAdd).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickOperator(v);
}
});
view.findViewById(R.id.btnMinus).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickOperator(v);
}
});
view.findViewById(R.id.btnDivide).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickOperator(v);
}
});
view.findViewById(R.id.btnMultiply).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickOperator(v);
}
});
view.findViewById(R.id.btnEquals).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickEquals(v);
}
});
view.findViewById(R.id.btnPrevAns).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onClickAns(v);
}
});
return view;
}
public void onClickEquals(View view) {
getResult();
updateresultdisplay();
}
private boolean getResult() {
if (operator.equals("")) return false;
String[] operation = formuladisplay.split(Pattern.quote(operator));
if (operation.length < 2) return false;
if (operator.equals("√")) {
result = String.valueOf(res.format(sqrtOp(operator,operation[1])));
resultdisplay = result;
prevAnswer = result;
result = "";
}
else {
result = String.valueOf(res.format(simpleOp(operation[0],operation[1],operator)));
resultdisplay = result;
prevAnswer = result;
result = "";
}
return true;
}
public double simpleOp(String a,String b,String op) {
switch (op) {
case "+":
return Double.valueOf(a) + Double.valueOf(b);
case "-":
return Double.valueOf(a) - Double.valueOf(b);
case "x":
return Double.valueOf(a) * Double.valueOf(b);
case "÷":
return Double.valueOf(a) / Double.valueOf(b);
default:
return -1;
}
}
private void updateformuladisplay() {
formulascreen.setText(formuladisplay);
}
private void updateresultdisplay() {
resultscreen.setText(resultdisplay);
}
public void onClicksqrt(View view) {
Button b = (Button) view;
operator = b.getText().toString();
formuladisplay += operator;
updateformuladisplay();
}
public void onClickDel(View view) {
if (formuladisplay.length() >= 1) {
formuladisplay = formuladisplay.substring(0,formuladisplay.length() - 1);
updateformuladisplay();
}
}
private void clear() {
formuladisplay = "";
resultdisplay = "";
}
public void onClickClear(View view) {
clear();
updateformuladisplay();
updateresultdisplay();
}
public void onClickNumber(View view) {
//if (!(result.equals(""))) {
// clear();
//updateformuladisplay();
//}
Button b = (Button) view;
if (formuladisplay.length() >= 0 && formuladisplay.length() <= 17) {
formuladisplay += b.getText();
updateformuladisplay();
}
else {
updateformuladisplay();
}
}
public void onClickOperator(View view) {
Button b = (Button) view;
operator = b.getText().toString();
formuladisplay += operator;
updateformuladisplay();
}
public double sqrtOp(String op,String a) {
switch (op) {
case "√":
return Math.sqrt(Double.valueOf(a));
default:
return -1;
}
}
public void onClickAns(View view) {
Button b = (Button) view;
if (formuladisplay.length() >= 0 && formuladisplay.length() <= 10) {
formuladisplay += prevAnswer;
updateformuladisplay();
}
else {
updateformuladisplay();
}
}
}
Solution
Use stack data structures to evaluate expressions Try this simple class
And add the sqrt operation in the evaluatepostfix method
public class InfixPostfixEvaluator {
/**
* Operators in reverse order of precedence.
*/
private static final String operators = "-+/*";
private static final String operands = "0123456789";
public int evalInfix(String infix) {
return evaluatePostfix(convert2Postfix(infix));
}
public String convert2Postfix(String infixExpr) {
char[] chars = infixExpr.tocharArray();
Stack<Character> stack = new Stack<Character>();
StringBuilder out = new StringBuilder(infixExpr.length());
for (char c : chars) {
if (isOperator(c)) {
while (!stack.isEmpty() && stack.peek() != '(') {
if (operatorGreaterOrEqual(stack.peek(),c)) {
out.append(stack.pop());
} else {
break;
}
}
stack.push(c);
} else if (c == '(') {
stack.push(c);
} else if (c == ')') {
while (!stack.isEmpty() && stack.peek() != '(') {
out.append(stack.pop());
}
if (!stack.isEmpty()) {
stack.pop();
}
} else if (isOperand(c)) {
out.append(c);
}
}
while (!stack.empty()) {
out.append(stack.pop());
}
return out.toString();
}
public int evaluatePostfix(String postfixExpr) {
char[] chars = postfixExpr.tocharArray();
Stack<Integer> stack = new Stack<Integer>();
for (char c : chars) {
if (isOperand(c)) {
stack.push(c - '0'); // convert char to int val
} else if (isOperator(c)) {
int op1 = stack.pop();
int op2 = stack.pop();
int result;
switch (c) {
case '*':
result = op1 * op2;
stack.push(result);
break;
case '/':
result = op2 / op1;
stack.push(result);
break;
case '+':
result = op1 + op2;
stack.push(result);
break;
case '-':
result = op2 - op1;
stack.push(result);
break;
}
}
}
return stack.pop();
}
private int getPrecedence(char operator) {
int ret = 0;
if (operator == '-' || operator == '+') {
ret = 1;
} else if (operator == '*' || operator == '/') {
ret = 2;
}
return ret;
}
private boolean operatorGreaterOrEqual(char op1,char op2) {
return getPrecedence(op1) >= getPrecedence(op2);
}
private boolean isOperator(char val) {
return operators.indexOf(val) >= 0;
}
private boolean isOperand(char val) {
return operands.indexOf(val) >= 0;
}
}
For details, please read http://willcode4beer.com/design.jsp?set=evalInfix
http://www.java2novice.com/data-structures-in-java/stacks/infix-expression/
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