Java ,Stack Calculator works fine if I manually push values to stack, but not if I push them using Scanner

Question

I have to to a calculator that adds, subtract, multiply and divide the numbers one by one to a stack, and at the end it will show the result of all operations. Example.

Input:10 Input:+ Input:10 Input:= Output: 10+10=20

I tried to do it by manually pushing the numbers and operators, and it worked fine, for adding and subtracting only. (here is the code).

 public static void main(String[] args) {
    Stack<String> stack = new Stack();
    stack.push("10");
    stack.push("+");
    stack.push("10");
    stack.push("-");
    stack.push("20");
    stack.push("+");
    stack.push("1");
    stack.push("=");
    int result=0;
    int i;
    int result=0;
    for(i=0;i<stack.size();i++){
        if (stack.elementAt(i)== "+"){
           //does get in

I checked in the second code that the stack is similar to the one on the first code, and it is similar. For some reason, it doesn't want to go through the if statement, even though it is equal to "+" or "-".

Stack<String> stack = new Stack();
    Scanner sc = new Scanner(System.in);
    while(sc.hasNext()){
        String s1 = sc.next();
        stack.push(s1);
        if(s1.equals("=")) {
            break;
        }
    }
    int i;
    int result=0;
    for(i=0;i<stack.size();i++){
        System.out.print(stack.elementAt(i));
    }
    for(i=0;i<stack.size();i++){
        if (stack.elementAt(i)=="+"){
        //doesn't get in

'Not if I push them using Scanner' is meaningless. – user207421 Oct 18 '17 at 06:09 — user207421, Oct 18 '17 at 06:09

score 0 · Accepted Answer · answered Oct 18 '17 at 04:14

0

The problem with your code is in this line

if (stack.elementAt(i)== "+")

The stack takes String types of arguements. For comparision you should use

if(stack.elementAt(i).equals("+"))

Similarly , do the same for "-".

answered Oct 18 '17 at 04:14

Karan

448
4
9

Fixed!! thank you, you saved my life! – La rrorra Oct 18 '17 at 04:16

Java ,Stack Calculator works fine if I manually push values to stack, but not if I push them using Scanner

1 Answers1