Array based stack implementation

[raunaak]

Hi all, I am new to C++ and I tried to implement array based stack.
Here is my code. It shows RUN FAILED on running it. Please help me solve this issue. Also, I have removed all the exceptions for stack over flow and under flow to specifically tackle the main issue.

#include<iostream>
#include<string>
using namespace std;
class StackArray{
private:
    int top;
    int capacity;
    int* array;
public:
    StackArray(){
        int top = 0;
        capacity = 10;
        array = new int[capacity];

    }
    StackArray(int cap){
        int top = 0;
        capacity = cap;
        array = new int[capacity];
    }
    void push(int value){
        cout<<"pushing into stack"<<endl;
        array[top]=value;  top++;
        cout<<"pushed into stack"<<endl;
    }
    int pop(){
        return array[top]; top--;
    }
    int peek(){
        return array[top];
    }
    int size(){
            return top;
    }
};

int main(){
    StackArray stack(5);
    for(int i=1; i<=4;i++)stack.push(i);    
    return 0;
}

[TheIdeasMan]

Hi,

First stop see if it compiles:

 In constructor 'StackArray::StackArray()': 
11:13: warning: unused variable 'top' [-Wunused-variable] 
In constructor 'StackArray::StackArray(int)': 
17:13: warning: unused variable 'top' [-Wunused-variable] 
In function 'int main()': 
38:16: warning: 'stack.StackArray::top' is used uninitialized in this function [-Wuninitialized]

On lines 11 and 17 you are re-declaring a local top variable, which provides confusion with the member variable with the same name.

In C++11, one can assign values in the class declaration:

class StackArray{
private:
    std::size_t top = 0; // assignment here is the same as a member initialization list
    std::size_t  capacity =10;
    int* array = new int[capacity]; // should avoid new, use smart pointers instead std::unique_ptr
public:
    StackArray() = default; // use compiler generated constructor
    StackArray(int capacityArg)
          : //colon introduces a member initialization list - google that :+)
          top(0),
          capacity(capacityArg),
          array (new int[capacity])
          {} // nothing to do here
    ~StackArray() {delete[] array;} // each new must be accompanied by a delete

See if that works :+)

[Chervil]

That code gave three compiler warnings for me.

Line 11: [Warning] unused variable 'top' [-Wunused-variable]
Line 17: [Warning] unused variable 'top' [-Wunused-variable]
Line 38: [Warning] 'stack' is used uninitialized in this function [-Wuninitialized]

At lines 11 and 17 a local variable top is declared instead of using the member variable declared at line 6.

There is also unreachable code, top--; at line 27 can never be executed.

There are a few other issues too, but I'll leave those for now.

[raunaak]

@TheIdeasMan and Chervil thanks a lot!! It works now :)