A stack of words in C (Sentence Palindrome)

[albim1998]

I was given this problem and I needed to create a code for it. So we have a string which is inputed by the user and then the code needs to check if the sentence is a palindrome or not ( the symmetric words to the middle of the sentence should be the same. But we should implement this using a stacks. I am familiar with functions pop() and push() (even thought I have not used them below). What I have thought until now is that I take the strings and create a stack of words out of this strings and use that stack to check if the sentence is a palindrome. I am stuck now and I can't really think of anything else. Help would be much appreciated.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
struct stack
{
    char s[30];
    struct stack *next;
};
 
typedef struct stack STACK;
 
struct top
{
    int num;
    struct stack *top;
};
 
typedef struct top TOP;
 
void create_stack(TOP *s, char str[1000])
{
    char temp1[30];
    int i=0, j=0;
 
    STACK *temp;
    temp=(STACK*)malloc(1*sizeof(STACK));
 
    while(1)
    {
        if(str[i]!=' ' && str[i]!='\0')
        {
            temp1[j]=str[i];
            j++;
        }
        else
        {
            temp1[j]='\0';
            strcpy(temp->s,temp1);
            printf("%s\n", temp->s);
 
            if(s->top==NULL)
            {
                s->top=temp;
                s->num=1;
            }
            else
            {
                temp->next=s->top;
                s->top=temp;
                s->num++;
            }
            j=0;
        }
        if(str[i]=='\0')
        {
            break;
        }
        i++;
    }
}
 
void move_cursor(STACK *cursor, int pos)
{
    while (pos!=0)
    {
        cursor=cursor->next;
        pos--;
    }
}
 
void compare(TOP *s)
{
    STACK *cursor1, *cursor2;
    cursor1=s->top;
    cursor2=s->top;
    int cursor_move1, cursor_move2, i=0, check=1;
 
    if(s->num%2==0)
    {
        cursor_move1=s->num/2;
        cursor_move2=(s->num/2)+1;
 
        while (i!=cursor_move1)
        {
            cursor1=s->top;
            cursor2=s->top;
            move_cursor(cursor1, i);
            move_cursor(cursor2, cursor_move2);
 
            if(strcmp(cursor1->s,cursor2->s)!=0)
            {
                check=0;
                break;
            }
            else
            {
                i++;
                cursor_move2++;
            }
        }
    }
 
    if(check==0)
        printf("%d Neg", check);
    else
        printf("1Pos");
}
 
void display(TOP *top)
{
    STACK *cursor;
    cursor=top->top;
 
    while(cursor->next==NULL)
    {
        printf("%s pos\n ", cursor->s);
 
        cursor=cursor->next;
    }
}
 
int main()
{
    char input[1000];
    TOP top;
    top.num=0;
    top.top=NULL;
 
    fgets(input, 100, stdin);
 
    input[strlen(input)-1]='\0';
 
    create_stack(&top, input);
 
    printf("%d \n ", top.num);
 
    display(&top);
    printf("---------------------------------------------------------\n");
    compare(&top);
 
 
    return 0;
}
 

[weaknessforcats]

Palindromes read backwards and forwards using the same letters:

A man a plan a canal Panama

and not the same words.


To use your stack approach read the string from left to write and push() each letter onto a stack. Then read the string from right to left and push each letter onto a second stack. Finally, pop each stack repeatedly and compare corresponding letters. If all letters match, you have a palindrome.

BTW: Use tolower() to be sure all stack entries are in lower case.