adding data to a stack implemented using 2 structs in C: moving pointers -

i'm struggling move pointer 1 element of stack next. have completed implementation. last element of stack given otherwise nothing try seems work. compiler gives error next undeclared (first use of function) on line pnewnode->next=next

relevant code below:

void push( topstack *ts, int val) {     if(ts->num==0)     {         stack *pnewnode;         pnewnode=(stack*)malloc(sizeof(stack));         pnewnode->val=val;         pnewnode->next=null;         ts->top=pnewnode;     }     else if(ts->num!=0)     {         stack *pnewnode;         pnewnode=(stack*)malloc(sizeof(stack));         pnewnode->val=val;         pnewnode->next=next;         ts->top=pnewnode;     } } 

the structs defined here:

typedef struct stack_elem {     int val;     struct stack_elem *next; } stack;  //struct contains pointer top of stack  typedef struct {     int num; //num of elements in stack     stack *top;; //top of stack } topstack; 

i have relevant prototypes functions below, structs in header file. ease of reading have included think relevant code can provide more if needed.

please modify code in else part pnewnode->next=ts->top;

void push( topstack *ts, int val) {     if(ts->num==0)     {        stack *pnewnode;        pnewnode=(stack*)malloc(sizeof(stack));        pnewnode->val=val;        pnewnode->next=null;        ts->top=pnewnode;    }    else if(ts->num!=0)    {        stack *pnewnode;        pnewnode=(stack*)malloc(sizeof(stack));        pnewnode->val=val;        pnewnode->next=ts->top;        ts->top=pnewnode;    } }