Thread: cannot understand sense of a warning

hello everybody!
I wrote simple functions to manage a stack, which I had already used and which I saw are very similar (let's say identical) to those shown in Deitel's book:

Code:

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

struct stackNode{
	char data;
	struct StackNode *nextPtr;
};
typedef struct stackNode StackNode;
typedef StackNode *StackNodePtr;

void push (StackNodePtr *topPtr, char value);
char pop (StackNodePtr *topPtr);
int isEmpty(StackNodePtr topPtr);
void printStack (StackNodePtr topPtr);

int main()
{
	srand(time(NULL));
	int i;
	StackNodePtr topPtr=NULL;
	for (i=0;i<10;i++)
	{
		push (&topPtr,'a'+rand()%26);
		printStack(topPtr);
	}
	for (i=0;i<10;i++)
	{
		pop (&topPtr);
		printStack(topPtr);
	}
}

void push (StackNodePtr *topPtr,char value)
{
	StackNodePtr newPtr = (StackNodePtr)malloc(sizeof(StackNode));
	if (newPtr!=NULL)
	{
		newPtr->data=value;
		newPtr->nextPtr=*topPtr;
		*topPtr=newPtr;
		
	}
	else
	{
		printf("Program run out of memory\n");
	}
}

char pop (StackNodePtr *topPtr)
{
	if (*topPtr==NULL)
	{
		return 0;
	}
	else
	{
		StackNodePtr tmpPtr=*topPtr;
		char ret = tmpPtr->data;
		*topPtr=tmpPtr->nextPtr;
		free(tmpPtr);
		return ret;
	}
}

int isEmpty(StackNodePtr topPtr)
{
	return topPtr==NULL;
}

void printStack (StackNodePtr topPtr)
{
	if (topPtr==NULL)
	{
		printf("Stack is empty\n");
	}
	else
	{
		while (topPtr!=NULL)
		{
			printf(" %c -->",topPtr->data);
			topPtr=topPtr->nextPtr;
		}
		printf(" NULL\n\n");
	}
}

after compiling i got this warning:

Code:

gcc e12_12.c -o e12_12
e12_12.c: In function ‘push’:
e12_12.c:43: warning: assignment from incompatible pointer type
e12_12.c: In function ‘pop’:
e12_12.c:63: warning: assignment from incompatible pointer type
e12_12.c: In function ‘printStack’:
e12_12.c:100: warning: assignment from incompatible pointer type

it doesn't like things like:

Code:

newPtr->nextPtr=*topPtr;

which also Deitel uses... Could anybody please explain me this?
Thanks a lot! bye

Originally Posted by xuftugulus

Code:

struct stackNode{
	char data;
	struct StackNode *nextPtr;
};

There was no resolution for that type at the point of declaration.
You should notice that the struct is called stackNode, and case matters.

i was sure to get trapped by some s... thank you very much!