First off, I'll be forthright in stating that this is a homework question.
I have to build an expression parser using the following code as my basis: Edit:
public class Interpreter {
public static Double parser(ST<String, Double> variables, String[] inputArray)
{
Double valueHolder;
Stack<String> ops = new Stack<String>();
Stack<Double> vals = new Stack<Double>();
for(int i = 0; i < inputArray.length; i++)
{
String input = inputArray[i];
if (input.equals("(")) ;
else if (input.equals("+")) ops.push(input);
else if (input.equals("-")) ops.push(input);
else if (input.equals("*")) ops.push(input);
else if (input.equals("/")) ops.push(input);
else if (input.equals("sqrt")) ops.push(input);
else if (input.equals(")"))
{
String op = ops.pop();
double v = vals.pop();
if (op.equals("+")) v = vals.pop() + v;
else if (op.equals("-")) v = vals.pop() - v;
else if (op.equals("*")) v = vals.pop() * v;
else if (op.equals("/")) v = vals.pop() / v;
else if (op.equals("sqrt")) v = Math.sqrt(v);
vals.push(v);
}
else if (input.matches("\\D"))
{
valueHolder = variables.get(inputArray[i]);
vals.push(valueHolder);
}
else vals.push(Double.parseDouble(input));
}
return vals.pop();
}
public static String[] getValue(ST<String, Double> variables, String[] inputArray)
{
Double keyHolder;
Double valueHolder;
for(int i = 0; i < inputArray.length; i++)
{
if(variables.contains(inputArray[i]))
{
keyHolder = variables.get(inputArray[i]);
inputArray[i] = keyHolder.toString();
}
else if (!variables.contains(inputArray[i]))
{ if (inputArray[i].matches("\\D")) //if letter
{ if (!inputArray[i].equals("=")) //if not "="
{for (int j = i + 1; j < inputArray.length; j++) //next element
{ if (inputArray[j].matches("\\D")) //if letter
{if (!inputArray[j].matches("=")) //if not "="
{
//get values and do math
}
}
else if (inputArray[j].matches("\\d")) // if digit
{ if (j + 1 >= inputArray.length)
{
valueHolder = Double.parseDouble(inputArray[j]);
variables.put(inputArray[i], valueHolder);
}
else parser(variables, inputArray); //if
}
}
}
}
}
}
return inputArray;
}
public static void main(String[] args)
{
ST<String, Double> variables = new ST<String, Double>();
while(!StdIn.isEmpty())
{
String input = StdIn.readLine();
String[] inputArray = input.split("\\s+"); // read a line and split it by whitespace
inputArray = getValue(variables, inputArray); // remove any variables and replace with their associated values
double y = parser(inputArray);
System.out.println(y);
}
}
}
Console input would be something like:
A = 5
B = 10
C = A + B
D = C * C
print(D)
In this case, the output from the console would be 225. My problem is that I cannot figure out how to split the input between the symbol table's keys and values. The API for inputting keys and values is void put(Key key, Value v) where if a key is set to null, the key is removed. Thanks in advanced.
It is not just string split, you need other checks too, like:
1) Split the string based on = pattern
if(stringValue.matches("="))
{
String[] valArray = stringValue.split("=");
}
else
{
// do something else
}
This will give you an array of string. Now loop through string array and check for below conditions.
2) Check if there is numeric value present
ie: valArray[].matches("\d");
3) If numeric value is present, check if there is more than 1 occurrences of alphabet numeric values present (to see if there are more than 1 variables present)
This is to check if alphabet is present in any of split strings >> valArray[].matches("\D");
4) Finally, if there is only 1 numeric value and 1 alphanumeric value present, store key and value.
5) If there are more than 1 occurrences of empty variables, then you will need to skip the operation(plus, minus ...) until you have variable value present in key-value array.
You can check this by checking your key-value pair array. You don't store key-value if the value if empty.
6) If = is not present then check for print in the string and do the print operation.
ie:
if(stringValue.matches("print"));
{
//Do something
}
Note: stringValue is your console input line.