Accessing multiple stacks using struct in c

Question

To be specific, I wanted to access multiple stacks with the purpose in mind to pop an element from one stack and push it into the other stack. So, I decided to access them using structures (struct). Consider the following code,

    #define MAX 100
    #include <stdio.h>
    #include <string.h>

    struct bag
    {
    int top;
    int arr[MAX];
    }harry,monk;

    int pop(struct bag name);
    void push(int data,struct bag name);

    int main()
    {
    int i,temp;
    harry.top=-1;
    monk.top=-1;
    push(3,harry);
    push(1,harry);
    push(1,harry);
    push(4,harry);

    temp=pop(harry);
    push(temp,monk);

    temp=pop(harry);
    push(temp,monk);

    for (i=0;i<4;i++)
    printf("%d\t%d\n",harry.arr[i],monk.arr[i]);
    return 0;
    }

    int pop(struct bag name)
    {
    int temp=name.arr[name.top];
    name.top=(name.top)-1;
    return temp;
    }

    void push(int data,struct bag name)
    {
    name.top=(name.top)+1;
    name.arr[name.top]=data;
    }

After analysing the code I found that each time I called function,

    void push(int data,struct bag name)

the value of the name.top was changed to from -1 to 0 but was reverted back to -1 when it was called again. Hence any vaue assigned to harry.arr[harry.top] was ultimately assigned to the array harry.arr[-1]. So, anyone out there with any ideas?

please indent your code

four_lines
– four_lines

2017-06-09 18:50:38 +00:00
Commented Jun 9, 2017 at 18:50 — four_lines
– four_lines, Commented Jun 9, 2017 at 18:50

user8138809 · Accepted Answer · 2017-06-09 18:55:33Z

1

Use pointers, as now you are passing the parameters its gets copied as a local parameters inside the function thus original pass value remains unchanged .

answered Jun 9, 2017 at 18:55

user8138809

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Comments

Easton Bornemeier · Accepted Answer · 2017-06-09 18:52:46Z

0

I'm pretty sure it's because you are never actually modifying the 'stacks' in your functions. C is pass by value, meaning you will have to return the struct 'name' and set it equal to harry and monk within your main.

Such as:

harry = push(3,harry);

Additionally you can use pointers to simulate a pass by reference scenario like what you are intending with your current code.

answered Jun 9, 2017 at 18:52

Easton Bornemeier

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