Push and Pop a string on the stack

[ami_31]

Hi All!
I want to push a string on the stack and read it in reverse order which can be done by pop function. But I m not able to do so.
Pls can you help me finding out where I am gonig wrong.

below is my code:

insert

#define _CRT_SECURE_NO_WARNINGS

// stack.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// self-referential structure
struct stackNode
{   
  char* data;
  struct stackNode *pNext;
   
};

typedef struct stackNode StackNode;
typedef StackNode *StackNodePtr;

// function prototypes
void push( StackNodePtr *pTop, char info[100] );
char* pop( StackNodePtr *pTop);
char isEmpty( StackNodePtr pTop );
void printStack( StackNodePtr pCurrent );

int main( void )
{ 
   StackNodePtr pStack = NULL;
   char string1[100];
   
  
   
  
  puts("Enter the string:");
  gets(string1);
  
   push( &pStack, string1 );
   printStack( pStack );

   
   printf("The popped value is %s", pop(&pStack));
	
      return 0;
}
     

void push( StackNodePtr *pTop, char info[100] )
{ 
   StackNodePtr pNew;

   pNew = malloc( sizeof( StackNode ) );

   if ( pNew != NULL )
   {  
      pNew->data = info;
      pNew->pNext = *pTop; // insert at top of stack
      *pTop = pNew;
   }
   else
   {
      printf( "%s not inserted. No memory available.\n", info );
   }
} 

char* pop( StackNodePtr *pTop)
{ 
   StackNodePtr pTemp;
   
   char *sPopValue = {0};

   pTemp = *pTop; // attach a pointer to element to be removed
   sPopValue = ( *pTop )->data; 
  printf("popped item is %s", sPopValue);
   *pTop = ( *pTop )->pNext; // remove at top of stack
   free( pTemp ); // release this memory and set it free!
   
   return sPopValue;

   if(*pTop == NULL)
   {
	   printf("Stack is empty");
   }
  
}

// output stack contents to the console
void printStack( StackNodePtr pCurrent )
{ 
   if ( pCurrent == NULL )
   {
      printf( "The stack is empty.\n\n" );
   }
   else
   { 
      printf( "The stack is:\n" );

      while ( pCurrent != NULL )
	  { 
         printf( "%s -> ", pCurrent->data );
         pCurrent = pCurrent->pNext; // move to next element
      }
      printf( "NULL\n\n" );
   } 
}

char isEmpty( StackNodePtr pTop )
{ 
   return pTop == NULL;
}

[itsme86]

To start with, this small snippet of code has some problems:

   StackNodePtr pStack = NULL;
   char string1[100];
   
  
   
  
  puts("Enter the string:");
  gets(string1);
  
   push( &pStack, string1 );

1) You're defining pStack as a StackNodePtr, but you really just want it to be a StackNode. Then drop the NULL initialization and, instead, initialize the members of pStack.

2) Never use gets().

[hk_mp5kpdw]

char* pop( StackNodePtr *pTop)
{ 
    StackNodePtr pTemp;
   
    char *sPopValue = {0};

    pTemp = *pTop; // attach a pointer to element to be removed
    sPopValue = ( *pTop )->data; 
    printf("popped item is %s", sPopValue);
    *pTop = ( *pTop )->pNext; // remove at top of stack
    free( pTemp ); // release this memory and set it free!
   
    return sPopValue;

    if(*pTop == NULL)
    {
        printf("Stack is empty");
    }
  
}

Code in red is unreachable because of the return statement just above it. Would have thought the compiler would complain to you about that one.

Hi All!
I want to push a string on the stack and read it in reverse order which can be done by pop function. But I m not able to do so.
Pls can you help me finding out where I am gonig wrong.

The way your stack is setup seems to be geared towards storing and printing entire strings, not individual characters. And even then, its flawed since what you are storing on the stack is a pointer to a local value (info) which would likely result in the stack - if you ever called it twice or more - appearing to store multiple copies of whatever the last string was pushed onto the stack.

You stack needs to store individual characters not entire strings. When you push the string, what you really need to do is push each individual character onto the stack. This will require some redesign.

[ami_31]

Thanks all for the quick reply.
@hk_mp5kpdw: For storing individual characters, do I need to use a for loop?
I tried using a for loop and entering the string but then after pushing the whole string my stack stores only the last word which I enter.
eg: if I enter "This is a test", and I enter 1 word in one incrementation of fr loop. My stack shows: test->test->test->NULL

[hk_mp5kpdw]

I tried using a for loop and entering the string but then after pushing the whole string my stack stores only the last word which I enter.
eg: if I enter "This is a test", and I enter 1 word in one incrementation of fr loop. My stack shows: test->test->test->NULL

That's exactly what I already explained is happening in my previous post:

And even then, its flawed since what you are storing on the stack is a pointer to a local value (info) which would likely result in the stack - if you ever called it twice or more - appearing to store multiple copies of whatever the last string was pushed onto the stack.

For storing individual characters, do I need to use a for loop?

Yes, you read the entire string into some buffer, probably fgets would be best. Then you iterate (loop) through that buffer character by character till the end of the string and push individual characters onto your stack.