Pretty much i can convert from infix to postfix really well and that is nto the problem
i need help with the postfix evaluation
also i dont think my evaluate method is correct
i have two push methods, one for char and one for int.
i really am stuck and not giving it much thought now :( , been working on it for 3 hours
if possible can someone try to help me shape the code if its correct to print the postfix and the the evaluation
but yah first i need to evaluate
also it would be cool if i could just evaluate the input directly .
so basically it is not necessary to evaluate the postfix
all i need is to show the postfix and the evaluation of the input if its too hard to evaluate the postfix.
please do help.
thank you in advance
import java.io.*;
class StackX
{
private int maxSize;
private char[] stackArray;
private int[] stackArray1;
private int top;
public StackX(int s)
{
maxSize = s;
stackArray = new char[maxSize];
top = -1;
}
public void push(char j)
{ stackArray[++top] = j; }
public void push1(int j)
{ stackArray1[++top] =j ; }
public char pop()
{ return stackArray[top--]; }
public char peek()
{ return stackArray[top]; }
public boolean isEmpty()
{ return (top == -1); }
public int size()
{ return top+1; }
public char peekN(int n)
{ return stackArray[n]; }
} // end class StackX used from lab1
class InToPost // infix to postfix conversion borrowed from book
{
private StackX theStack;
private String input;
private String output = "";
public InToPost(String in) // constructor
{
input = in;
int stackSize = input.length();
theStack = new StackX(stackSize);
}
public String doTrans() // algorithm that does translation with cases
{
for(int j=0; j<input.length(); j++)
{
char ch = input.charAt(j);
switch(ch)
{case '+':gotOper(ch, 1); break;
case '-':gotOper(ch, 1); break;
case '*':gotOper(ch, 2); break;
case '/':gotOper(ch, 2); break;
default :output = output + ch; break; //writes to output
} // end of switch
} // end for loop
while( !theStack.isEmpty() ) // pop remaining operators at the end
{
output = output + theStack.pop(); // write to output
}
return output; // return postfix
}
//--------------------------------------------------------------
public void gotOper(char opThis, int prec1)
{
while( !theStack.isEmpty() )
{
char opTop = theStack.pop();
if(1==1 )
{
int prec2;
if(opTop=='+' || opTop=='-') // find new op prec
prec2 = 1;
else
prec2 = 2;
if(prec2 < prec1)
{
theStack.push(opTop);
break;
}
else
output = output + opTop;
}
} // end while loop
theStack.push(opThis);
}
public void evaluate() {
int x;
int y;
for (int j = 0; j < output.length(); j++) {
int result = 0;
char ch = output.charAt(j);
switch (ch) {
case '+':
x = theStack.pop();
y = theStack.pop();
result = x + y;
theStack.push1(result);
break;
case '-':
x = theStack.pop();
y = theStack.pop();
result = x - y;
theStack.push1(result);
break;
case '*':
x = theStack.pop();
y = theStack.pop();
result = x * y;
theStack.push1(result);
break;
case '/':
x = theStack.pop();
y = theStack.pop();
result = x / y;
theStack.push1(result);
break;
default:
theStack.push(ch);
break;
}
}
System.out.println(theStack.pop());
}
}
class lab2
{
public static void main(String[] args) throws IOException
{
String input, output;
while(true)
{
System.out.print("Enter infix: ");
System.out.flush();
input = getString();
if( input.equals("") )
break;
InToPost theTrans = new InToPost(input);
output = theTrans.doTrans();
System.out.println("Postfix is " + output );
}
}
public static String getString() throws IOException
{
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr);
String s = br.readLine();
return s;
}
}
