Expression Evaluation

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package Question2;

import Question1.MyStack;
import java.util.Scanner;

/**
 *
 * @author CSC2017
 */
public class EvalExpression {
    private static MyStack<Integer> numStack = new MyStack<>();
    private static MyStack<Character> opStack = new MyStack<>();

    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        System.out.println("Enter Expression: ");
        String exprsion = s.nextLine();
        int value = eval(exprsion);
        System.out.println(exprsion+" = "+value);
    }
    public static int eval(String exprsion){
        int result = 0;
        for(char c:exprsion.toCharArray()){
            if((int)c <= 57 && (int)c >=48){
                //char c is a number
                numStack.push((int)c - 48);
            }else{
                //if not a number then an operator
                if(opStack.empty()){
                    //no operands pushed yet
                    opStack.push(c);
                }else{
                    //operands inside
                    char topOp = opStack.peek();
                    if(isHigherOperand(topOp,c)){
                        do{
                            topOp = opStack.pop();
                            int num1 = numStack.pop();
                            int num2 = numStack.pop();
                            int value = evalOperation(num2,topOp,num1);
                            numStack.push(value);
                            topOp = opStack.peek();
                        }while(isHigherOperand(topOp,c));
                        opStack.push(c);
                    }else{
                        opStack.push(c);                    }
                }
            }
        }
        if(!opStack.empty()){
            while(!opStack.empty()){
                char topOp = opStack.pop();
                int num1 = numStack.pop();
                int num2 = numStack.pop();
                int value = evalOperation(num2,topOp,num1);
                numStack.push(value);
            }
        }
        result = numStack.pop();
        return result;
    }
    public static boolean isHigherOperand(char firstOp,char secOp){
        //returns true if first operand greater than second
        if(firstOp == '*' || firstOp == '/') return true; //assuming the operaots are + - * /
        else return false;
    }
    public static int evalOperation(int num1,char topOp,int num2){
        int value = 0;
        switch(topOp){
            case '+':
                value = num1+num2;
                break;
            case '-':
                value = num1-num2;
                break;
            case '*':
                value = num1*num2;
                break;
            case '/':
                value = num1/num2;
                break;
            default:
                value = 0;
                break;
        }
        return value;
    }
}