Код калькулятора на Java
Код калькулятора на Java
 
Представлен исходный код калькулятора на языке программирования Java

public class Calc2 {
static enum TOKEN {
PLUS, MINUS, MUL, DIV, NUMBER, LP, RP, END, FUNCTION;
}
double expr() {
double left = term();
while (true) {
switch (curr_tok) {
case PLUS:
left += term();
break;
case MINUS:
left -= term();
break;
default:
return left;
}
}
}
double term() {
double left = prim();
while (true) {
switch (curr_tok) {
case MUL:
left *= prim();
break;
case DIV:
left /= prim();
break;
default:
return left;
}
}
}
double prim() {
get_token();
switch (curr_tok) {
case NUMBER:
double v = number_value;
get_token();
return v;
case MINUS:
return -prim();
case LP:
double e = expr();
if (curr_tok != TOKEN.RP)
return error(")expected");
return e;
case FUNCTION:
String f = function_name;
get_token();
if (curr_tok != TOKEN.LP)
return error("( expected");
double z = prim();
if (curr_tok != TOKEN.RP)
return error(") expected");
if ("sin".equals(f)) {
return Math.sin(z);
} else {
return error("unknown function");
}
default:
return error("primary expression expected");
}
}
double error(String msg) {
error_msg = msg;
return Double.NaN;
}
TOKEN curr_tok;
double number_value;
String function_name;
String error_msg;
String input;
int pos;
void get_token() {
if (pos >= input.length()) {
curr_tok = TOKEN.END;
return;
}
char x = input.charAt(pos++);
switch (x) {
case '+':
curr_tok = TOKEN.PLUS;
break;
case '-':
curr_tok = TOKEN.MINUS;
break;
case '*':
curr_tok = TOKEN.MUL;
break;
case '/':
curr_tok = TOKEN.DIV;
break;
case '(':
curr_tok = TOKEN.LP;
break;
case ')':
curr_tok = TOKEN.RP;
break;
default:
if (Character.isDigit(x) || x == '.') {
curr_tok = TOKEN.NUMBER;
String s = "" + x;
while (pos < input.length() && (Character.isDigit(input.charAt(pos)) || input.charAt(pos) == '.')) {
s += input.charAt(pos);
++pos;
}
number_value = Double.parseDouble(s);
} else if (Character.isLetter(x)) {
curr_tok = TOKEN.FUNCTION;
String s = "" + x;
while (pos < input.length() && Character.isLetter(input.charAt(pos))) {
s += input.charAt(pos);
++pos;
}
function_name = s;
}
}
}
public static void main(String[] args) {
Calc2 calc = new Calc2();
calc.input = "sin(1)";
calc.pos = 0;
double res = calc.expr();
if (Double.isNaN(res)) {
System.out.println(calc.error_msg);
} else {
System.out.println(res);
}
}
}

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