import java.util.Scanner;
public class CalculationsForGraphingCalculator {
public static void main(String[] args) {
System.out.println(
"Welcome to the data points calculator! This program creates a table of values based on a given formula.");
System.out.println();
System.out.print("Please insert your equation in terms of x. Separate each term with a space (Ex: x^2 + 2*x + 3 You MUST include all signs (2x should be 2*x)): y = ");
Scanner scan = new Scanner(System.in);
String formula = scan.nextLine();
String revisedFormula = formula;
System.out.println();
System.out.print("Left bound of your domain? ");
double leftBound = scan.nextDouble();
System.out.println();
System.out.print("Right bound of your domain? ");
double rightBound = scan.nextDouble();
System.out.println();
System.out.print("Step of your function (the increments at which the function is evaluated at: ");
double step = scan.nextDouble();
System.out.println(" x " + " y");
System.out.println("_____________________________");
for (double i = leftBound; i <= rightBound; i += step) {
String input = Double.toString(i);
revisedFormula = formula.replaceAll("x", input);
System.out.println(input + " | " + eval(revisedFormula));
}
scan.close();
}
//https://stackoverflow.com/questions/3422673/evaluating-a-math-expression-given-in-string-form
public static 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 | functionName 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 *= parseFactor(); // multiplication
else if (eat('/')) x /= parseFactor(); // division
else return x;
}
}
double parseFactor() {
if (eat('+')) return parseFactor(); // unary plus
if (eat('-')) return -parseFactor(); // unary minus
double x;
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 throw new RuntimeException("Unknown function: " + func);
} else {
throw new RuntimeException("Unexpected: " + (char)ch);
}
if (eat('^')) x = Math.pow(x, parseFactor()); // exponentiation
return x;
}
}.parse();
}
}
