I have made a program to implement stack but it is not working properly

Question

The code is not throwing any error but it is not taking the values that we pass in the enqueue function. Here is the code:

#include <bits/stdc++.h>
#include <climits>
using namespace std;

struct Queue{
    int *arr;
    int front , rear;
    int cap;
    Queue(int c){
        cap = c;
        front = -1;
        rear = -1;
        arr = new int[cap];
    }
    void enqueue(int x){
        if(rear == cap-1){
            cout<<"The array is full";
        }
        rear++;
        arr[rear] == x;
        cout<<arr[rear]<<endl;
    
        if(front == -1){
            front = 0;
        }
    }
    int dequeue(){
        int data;

        if(front == -1){`your text`
            cout<<"Array is empty";
            return INT_MIN;
        }
    

        data = arr[front];
        arr[front] = 0;
    
        if(front == rear){
            front = rear = -1;
        }
        else{
            front++;
        }
        return data;
    }
};
int main() {
    Queue q(3);

    q.enqueue(24);
    q.enqueue(30);
    q.enqueue(42);

    cout<<q.dequeue();
    return 0;
}

the enqueue function is taking some garbage value instead of the integer value that we are passing in the argument.

Move to this line `arr[rear] == x;` and think about it again. — Pepijn Kramer, Jan 17 '23 at 12:15
Unrelated : remove `#include ` it is not standard C++. And stop using `using namespace std;` replace new int[] with std::vector (in C++ try to avoid manual new/delete), or use std::make_unique to avoid memory leaks (you have them now) — Pepijn Kramer, Jan 17 '23 at 12:17
In addition to what has been said above: Looking at `new int[cap]`, I have to ask: where is your `delete[]`? — Andrej Podzimek, Jan 17 '23 at 12:18
[What is a debugger and how can it help me diagnose problems?](https://stackoverflow.com/questions/25385173/what-is-a-debugger-and-how-can-it-help-me-diagnose-problems) — Jesper Juhl, Jan 17 '23 at 12:24

score 1 · Answer 1 · answered Jan 17 '23 at 12:17

Hi and welcome to Stackoverflow.

The problem is that you ignored your compiler warnings. Under https://godbolt.org/z/Pn1Mf115T i have thrown your code in an online compiler and it tells me/you:

<source>:20:19: warning: equality comparison result unused [-Wunused-comparison]
        arr[rear] == x;
        ~~~~~~~~~~^~~~
<source>:20:19: note: use '=' to turn this equality comparison into an assignment
        arr[rear] == x;
                  ^~
                  =
1 warning generated.
Compiler returned: 0

So the compiler tells you that you comparing instead of assigning the values. Thats the reason why your queue takes garbage values, it just never gets data assigned and the output is the uninitialized memory from your C-style array.

Rule of thumb: Do not ignore compiler warnings.

I have made a program to implement stack but it is not working properly

1 Answers1