我想编写一个程序，该程序采用一个中缀字符串并将其更改为后缀，然后求值后缀并打印答案；对于+-* / ^很容易，只需要运算符的优先级即可，但是我不知道对于sin cos log和其他数学函数应该怎么做。
private static String infixToPostfix(String infix) {
String[] exp = infix.split("");
Stack<String> stack = new Stack<>();
String result = "";
for (int i = 0; i < exp.length; i++){
if (exp[i].equals("(")) {
stack.push(exp[i]);
}
else if (isOperator(exp[i]))
{
while (!stack.isEmpty() && precedence(exp[i]) <= precedence(stack.getTop())){
result += stack.pop() + " ";
}
stack.push(exp[i]);
}
else if (exp[i].equals(")"))
{
while (!stack.isEmpty() && !stack.getTop().equals("(")){
result += stack.pop() + " ";
}
stack.pop();
}
else if (Character.isLetterOrDigit(infix.charAt(i)) || exp[i].equals(".")){
boolean haveDot = exp[i].equals(".");
String temp = haveDot ? "0." : exp[i];
while ((i + 1) < exp.length && (Character.isLetterOrDigit(infix.charAt(i + 1)) || exp[i + 1].equals("."))){
temp += exp[i + 1];
i++;
}
result += temp + " ";
}
}
while (!stack.isEmpty()){
result += stack.pop() + " ";
}
return result;
}
正在正常工作！
但是这个
private static Double postFixEvaluator(String[] postFix) {
Stack<Double> operands = new Stack<>();
double value = 0.0;
for (int str = 0; str < postFix.length; str++) {
if (postFix[str].trim().equals("")) {
continue;
}
switch (postFix[str]) {
case "+":
case "-":
case "*":
case "/":
case "^":
Double right = operands.pop();
Double left = operands.pop();
long intValue = 0;
switch (postFix[str]) {
case "+":
value = left + right;
break;
case "-":
value = left - right;
break;
case "*":
value = left * right;
break;
case "/":
value = left / right;
break;
case "^":
value = Math.pow(left, right);
break;
default:
break;
}
case "sin":
case "cos":
case "tan":
case "cot":
if (Character.isLetterOrDigit(Arrays.toString(postFix).charAt(str + 2))) {
str++;
break;
}
else{
Double oper = operands.pop();
switch (postFix[str]) {
case "sin":
value = Math.sin(oper);
break;
case "cos":
value = Math.cos(oper);
break;
case "tan":
value = Math.tan(oper);
break;
case "cot":
value = 1 / Math.tan(oper);
break;
}
}
operands.push(value);
break;
default:
operands.push(Double.parseDouble(postFix[str]));
break;
}
}
return operands.pop();
}
它不能正常工作。