Untitled

package com.example.myapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    Button b1, b2, b3, b4, b5, b6, b7, b8, b9, b0, bdot, bpi, bequal, bplus, bminus, bdiv, bmul, bac, bc, bb1, bb2, bln, bsin, bcos, btan, binv, bsqrt, bsquare, bfact, blog;
    TextView tvsec, tvmain;
    String pi = "3.14159265";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initializeViews();
        setButtonListeners();
    }

    private void initializeViews() {
        b1 = findViewById(R.id.b1);
        b2 = findViewById(R.id.b2);
        b3 = findViewById(R.id.b3);
        b4 = findViewById(R.id.b4);
        b5 = findViewById(R.id.b5);
        b6 = findViewById(R.id.b6);
        b7 = findViewById(R.id.b7);
        b8 = findViewById(R.id.b8);
        b9 = findViewById(R.id.b9);
        b0 = findViewById(R.id.b0);
        bac = findViewById(R.id.bac);
        bc = findViewById(R.id.bc);
        bb1 = findViewById(R.id.bb1);
        bb2 = findViewById(R.id.bb2);
        bpi = findViewById(R.id.bpi);
        bdot = findViewById(R.id.bdot);
        bequal = findViewById(R.id.bequal);
        bplus = findViewById(R.id.bplus);
        bminus = findViewById(R.id.bminus);
        bmul = findViewById(R.id.bmul);
        bdiv = findViewById(R.id.bdiv);
        binv = findViewById(R.id.binv);
        bsqrt = findViewById(R.id.bsqrt);
        bsquare = findViewById(R.id.bsquare);
        bfact = findViewById(R.id.bfact);
        bln = findViewById(R.id.bln);
        bsin = findViewById(R.id.bsin);
        bcos = findViewById(R.id.bcos);
        btan = findViewById(R.id.btan);
        blog = findViewById(R.id.blog);

        tvmain = findViewById(R.id.tvmain);
        tvsec = findViewById(R.id.tvsec);
    }

    private void setButtonListeners() {
        View.OnClickListener numberClickListener = new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Button button = (Button) v;
                tvmain.append(button.getText().toString());
            }
        };

        b1.setOnClickListener(numberClickListener);
        b2.setOnClickListener(numberClickListener);
        b3.setOnClickListener(numberClickListener);
        b4.setOnClickListener(numberClickListener);
        b5.setOnClickListener(numberClickListener);
        b6.setOnClickListener(numberClickListener);
        b7.setOnClickListener(numberClickListener);
        b8.setOnClickListener(numberClickListener);
        b9.setOnClickListener(numberClickListener);
        b0.setOnClickListener(numberClickListener);
        bdot.setOnClickListener(numberClickListener);

        bac.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                tvmain.setText("");
                tvsec.setText("");
            }
        });

        bc.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String val = tvmain.getText().toString();
                if (!val.isEmpty()) {
                    val = val.substring(0, val.length() - 1);
                    tvmain.setText(val);
                }
            }
        });

        bplus.setOnClickListener(operatorClickListener("+"));
        bminus.setOnClickListener(operatorClickListener("-"));
        bdiv.setOnClickListener(operatorClickListener("÷"));
        bmul.setOnClickListener(operatorClickListener("×"));

        bsqrt.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    String val = tvmain.getText().toString();
                    double r = Math.sqrt(Double.parseDouble(val));
                    tvmain.setText(String.valueOf(r));
                } catch (Exception e) {
                    showToast("Error: Invalid input for square root");
                }
            }
        });

        bb1.setOnClickListener(operatorClickListener("("));
        bb2.setOnClickListener(operatorClickListener(")"));
        bpi.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                tvsec.setText(bpi.getText());
                tvmain.append(pi);
            }
        });

        bsin.setOnClickListener(operatorClickListener("sin"));
        bcos.setOnClickListener(operatorClickListener("cos"));
        btan.setOnClickListener(operatorClickListener("tan"));
        binv.setOnClickListener(operatorClickListener("^(-1)"));
        bln.setOnClickListener(operatorClickListener("ln"));
        blog.setOnClickListener(operatorClickListener("log"));

        bfact.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    int val = Integer.parseInt(tvmain.getText().toString());
                    int fact = factorial(val);
                    tvmain.setText(String.valueOf(fact));
                    tvsec.setText(val + "!");
                } catch (Exception e) {
                    showToast("Error: Invalid input for factorial");
                }
            }
        });

        bsquare.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    double d = Double.parseDouble(tvmain.getText().toString());
                    double square = d * d;
                    tvmain.setText(String.valueOf(square));
                    tvsec.setText(d + "²");
                } catch (Exception e) {
                    showToast("Error: Invalid input for square");
                }
            }
        });

        bequal.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    String val = tvmain.getText().toString();
                    String replacedStr = val.replace('÷', '/').replace('×', '*');
                    double result = eval(replacedStr);
                    tvmain.setText(String.valueOf(result));
                    tvsec.setText(val);
                } catch (Exception e) {
                    showToast("Error: Invalid expression");
                }
            }
        });
    }

    private View.OnClickListener operatorClickListener(final String operator) {
        return new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                tvmain.append(operator);
            }
        };
    }

    private void showToast(String message) {
        Toast.makeText(getApplicationContext(), message, Toast.LENGTH_SHORT).show();
    }

    //Factorial function
    int factorial(int n) {
        return (n == 1 || n == 0) ? 1 : n * factorial(n - 1);
    }

    //eval function
    public double eval(final String str) {
        return new Object() {
            int pos = -1, ch;

            void nextChar() {
                ch = (++pos < str.length()) ? str.charAt(pos) : -1;
            }

            boolean eat(int charToEat) {
                while (ch == ' ') nextChar();
                if (ch == charToEat) {
                    nextChar();
                    return true;
                }
                return false;
            }

            double parse() {
                nextChar();
                double x = parseExpression();
                if (pos < str.length()) throw new RuntimeException("Unexpected: " + (char) ch);
                return x;
            }

            //Grammar:
            //expression = term | expression '+' term | expression '-' term
            //term = factor | term '*' factor | term '/' factor
            //factor = '+' factor | '-' factor | '(' expression ')'
            //        | number | factorName factor | factor '^' factor

            double parseExpression() {
                double x = parseTerm();
                for (; ; ) {
                    if (eat('+')) x += parseTerm(); //Addition
                    else if (eat('-')) x -= parseTerm(); //Subtraction
                    else return x;
                }
            }

            double parseTerm() {
                double x = parseFactor();
                for (; ; ) {
                    if (eat('*')) x *= parseTerm(); //Multiplication
                    else if (eat('/')) x /= parseTerm(); //Division
                    else return x;
                }
            }

            double parseFactor() {
                if (eat('+')) return parseFactor(); //Unary Plus
                if (eat('-')) return -parseFactor(); //Unary Minus

                double x = 0;
                int startPos = this.pos;
                if (eat('(')) { // Parentheses
                    x = parseExpression();
                    eat(')');
                } else if ((ch >= '0' && ch <= '9') || ch == '.') { // Numbers
                    while ((ch >= '0' && ch <= '9') || ch == '.') nextChar();
                    x = Double.parseDouble(str.substring(startPos, this.pos));
                } else if ((ch >= 'a' && ch <= 'z')) { // Functions
                    while ((ch >= 'a' && ch <= 'z')) nextChar();
                    String func = str.substring(startPos, this.pos);
                    x = parseFactor();
                    if (func.equals("sqrt")) x = Math.sqrt(x);
                    else if (func.equals("sin")) x = Math.sin(Math.toRadians(x));
                    else if (func.equals("cos")) x = Math.cos(Math.toRadians(x));
                    else if (func.equals("tan")) x = Math.tan(Math.toRadians(x));
                    else if (func.equals("log")) x = Math.log10(x);
                    else if (func.equals("ln")) x = Math.log(x);
                    else showToast("Error: Unknown function " + func);
                } else {
                    showToast("Error: Unexpected character");
                }
                if (eat('^')) x = Math.pow(x, parseFactor()); // Exponentiation
                return x;
            }

        }.parse();
    }
}