to implement stack of strings in C

Question

I want to implement a stack of strings wherein every element of a stack represents a string. For example I input names of people as elements. I have written the following code but the display is not working.

#include <stdio.h>
#include <stdlib.h>

#define max 5
struct stack{
    int top;
    char *stack[100];
};
typedef struct stack stack;

void push(struct stack *s)
{
    char element[20];
    if (s->top == max-1)
    {
        printf("Stack is full\n");
        return;
    }
    else
    {
        s->top+=1;
        printf("Enter the element to be pushed\n");
        scanf("%s",element);
        for(int i=0;element[i]!='/0';i++)
        *(s->stack[s->top])=element;
    }
}

void pop(struct stack *s)
{
    if (s->top == -1)
    {
        printf("Stack is empty\n");
        return;
    }
    else
    {        printf("The element deleted is %s\n",*(s->stack[s->top]));
        s->top-=1;
    }
}

void display(struct stack *s)
{
    if (s->top == -1)
    {
        printf("Stack is empty\n");
        return;
    }
    else
    {
        for (int i=0;i<=s->top;i++)
        {
            printf("%s\n",*(s->stack[i]));
        }
    }
}
int main()
{
    struct stack s;
    s.top=-1;
    int ch;
    for(;;)
    {
    printf("Enter your choice\n1.Push\n2.Pop\n3.Display\n4.Exit\n");
    scanf("%d",&ch);
    switch (ch)
    {
        case 1:
            push(&s);
            break;
        case 2:
            pop(&s);
            break;
        case 3:
            display(&s);
            break;
        case 4:
            goto a;
            break;
        default:
            printf("Invalid choice");
            break;
    }
    }
    a:
    return 0;
}

This is an example of the expected terminal : Enter your choice 1.Push 2.Pop 3.Display 4.Exit 1 Enter the element to be pushed john Enter your choice 1.Push 2.Pop 3.Display 4.Exit 1 Enter the element to be pushed maddy Enter your choice 1.Push 2.Pop 3.Display 4.Exit 3 The elements are: john maddy

*(s->stack[i]) looks like one de-reference too many. Compile with strict standard settings and pay attention to compiler warnings/errors. — Lundin
– Lundin, Commented Jan 16, 2023 at 7:24
It's not exactly the problem, but when you look at where the code is copying letters hoping to save them,, consider also adding a terminating \0 to make a "C string". — user17592432
– user17592432, Commented Jan 16, 2023 at 7:40
... but the display is not working. What does not working mean? — Gerhard
– Gerhard, Commented Jan 16, 2023 at 7:41
` goto a;` means break; will never execute. Rename a to a meaningful name if you are going to use goto. — Gerhard
– Gerhard, Commented Jan 16, 2023 at 7:45
scanf("%s",element); can overflow char element[20];. use scanf("%19s", element); — Gerhard
– Gerhard, Commented Jan 16, 2023 at 7:49

Gerhard · Accepted Answer · 2023-01-16 09:12:13Z

1

I looked only at the push() part of your code.

You have char *stack[100]; which is an array of 100 character pointers.
You need char stack[5][20]; which an array of 5 strings of 20 character each.

To save the strings in the stack you need to change the copy part of your code:

for(int i=0; element[i]!='\0'; i++)
  s->stack[s->top][i] = element[i];

This copies the string character for character onto the stack. strncpy() would be a better way of doing this.

strncpy(s->stack[s->top], element, 20);

Look at all the comments on your question as well for other problems and code smells. There a still still some other problems remaining.

edited Jan 16, 2023 at 9:12

answered Jan 16, 2023 at 9:02

Gerhard

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