G.M - 8 months ago 27

Android Question

I'm currently working on a school project (a small android game) and so far I've written a code which generates a random equation 2 seconds after the activity 'InGame' is launched and displays it in a textview. Another 5 seconds later, the second equation is generated and displayed in a different textview. Now the user has to decide if the second equation has a bigger result than the first one by either pressing the button 'bigger' or 'smaller'. If it was correct, the next equation should be displayed and it would go on like this until the user decided wrong.

Here is my code so far:

(Code for the first equation):

`// Generate random equation and display it in textview`

String[] operationSet = new String[]{"+", "-", "/", "*"};

String equation;

static double doubleAnswer1;

public void start1() {

Random random = new Random();

int numOfOperations = random.nextInt(2) + 1;

List<String> operations = new ArrayList<>();

for (int i = 0; i < numOfOperations; i++) {

String operation = operationSet[random.nextInt(4)];

operations.add(operation);

}

int numOfNumbers = numOfOperations + 1;

List<Integer> numbers = new ArrayList<>();

for (int i = 0; i < numOfNumbers; i++) {

int number = random.nextInt(10)+1;

numbers.add(number);

}

String equation = "";

for (int i = 0; i < numOfOperations; i++) {

equation += numbers.get(i);

equation += operations.get(i);

}

equation += numbers.get(numbers.size() -1);

TextView TextEquation = (TextView)findViewById(R.id.textView_first_equation);

TextEquation.setText(equation);

// Evaluate the result of the equation

double doubleAnswer1 = eval(equation);

String stringAnswer = Double.toString(doubleAnswer1);

TextView textAnswer = (TextView)findViewById(R.id.textView4);

textAnswer.setText(stringAnswer);

}

(Code for second equation (basically same as for first equation except the name of the strings and doubles are different)):

`String equation2;`

static double doubleAnswer2;

public void start2() {

Random random = new Random();

int numOfOperations = random.nextInt(2) + 1;

List<String> operations = new ArrayList<>();

for (int i = 0; i < numOfOperations; i++) {

String operation = operationSet[random.nextInt(4)];

operations.add(operation);

}

int numOfNumbers = numOfOperations + 1;

List<Integer> numbers = new ArrayList<>();

for (int i = 0; i < numOfNumbers; i++) {

int number = random.nextInt(10)+1;

numbers.add(number);

}

String equation2 = "";

for (int i = 0; i < numOfOperations; i++) {

equation2 += numbers.get(i);

equation2 += operations.get(i);

}

equation2 += numbers.get(numbers.size() -1);

TextView TextEquation = (TextView)findViewById(R.id.textView3);

TextEquation.setText(equation2);

// Evaluate the result of the equation

double doubleAnswer2 = eval(equation2);

String stringAnswer = Double.toString(doubleAnswer2);

TextView textAnswer = (TextView)findViewById(R.id.textView_result2);

textAnswer.setText(stringAnswer);

}

And here is my onCreate code:

`@Override`

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.ingame);

// Display first equation 2 seconds after the activity is launched

final Handler handler1 = new Handler();

handler1.postDelayed(new Runnable() {

@Override

public void run() {

start1();

}

}, 2000);

final Handler handler2 = new Handler();

handler2.postDelayed(new Runnable() {

@Override

public void run() {

start2();

}

}, 7000);

// Check if user was right or wrong

final Button buttonBigger = (Button)findViewById(R.id.button_bigger);

final Button buttonSmaller = (Button)findViewById(R.id.button_smaller);

View.OnClickListener listener = new View.OnClickListener() {

@Override

public void onClick(View v) {

if(v.equals(buttonBigger) && doubleAnswer1 < doubleAnswer2) {

Log.v("TAG", "you are right");

} else if(v.equals(buttonSmaller) && doubleAnswer1 > doubleAnswer2) {

Log.v("TAG", "you are right");

} else {

Log.v("TAG", "you are wrong");

}

}

};

buttonBigger.setOnClickListener(listener);

buttonSmaller.setOnClickListener(listener);

}

The app launches correctly and it also displays the first and second equation but when I press one of the button, it tells me in the logcat "you are wrong" but I decided 100% correct. However if I debug the app, it tells me that doubleAnswer1 and doubleAnswer2 are both = 0. That's why it allways tells me 'you are wrong'. I don't know how to fix this, maybe I need to store the doubleAnswer1 and doubleAnswer2 somewhere.

I really don't know what to do, so it would really help me if someone has an idea what to do.

If anything is unclear in my question, feel free to ask and I will try to clarify the problem.

Thank you already in advance for your help!

Answer

I think your problem lies here:

```
double doubleAnswer1 = eval(equation);
```

I did a quick internet search and did not find any native function called eval(). Instead you should look into Script Engine Manager for java:

```
ScriptEngineManager mgr = new ScriptEngineManager();
ScriptEngine engine = mgr.getEngineByName("JavaScript");
String foo = "40+2";
System.out.println(engine.eval(foo));
```

or exp4j which is shown here: Executing math equation in Android

Edit: change the following:

```
double doubleAnswer1 = eval(equation);
```

to:

```
doubleAnswer1 = eval(equation);
```

Similarly do the same for doubleAnswer2

Source (Stackoverflow)