Java – the calculator does not handle two operator equations
•
Android
I am developing a calculator application, and all functions have been turned off. The only problem is that when I enter an equation containing two arithmetic operators, it will fail. For example, if I enter "2 √ 9", it will return 3. If I enter "√ 92", it will be forced off 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();
}
}
}
resolvent:
Use stack data structures to evaluate expressions. Try this simple class. You can add sqrt operations to regular expressions
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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