infix to postfix using stacks as linked lists in C language

infix to postfix using stacks as linked lists in C language

i have written a program to convert infix to postfix using C language in
UBUNTU...but my program is not woarking properly can any one help??? MY
PROGRAM IS AS FOLLOWS
#include<stdio.h>
#include<stdlib.h>
char op[50];
struct node
{
char data;
struct node *next;
} *l1=NULL;
void push(char x) // pushes char into the linkedlist
{
if(l1==NULL)
{
l1=(struct node *)malloc(sizeof(struct node));
l1->data=x;
l1->next=NULL;
}
else
{
struct node *p;
p=(struct node *)malloc(sizeof(struct node));
p->data=x;
p->next=l1;
l1=p;
}
}
char pop() // pops char outof linkedlist
{
char c;
struct node *p;
if (l1==NULL)
{
printf("the stack is empty\n");
// exit(1);
}
else
{
c=l1->data;
p=l1->next;
free (l1);
l1=p;
}
return c;
}
void display(struct node *start)
{
{
int i=0;
struct node *p;
p=start;
if(p==NULL)
printf("Empty list");
else
{
while(p!=NULL)
{
printf("%c->",p->data);
p=p->next;
}
printf("NULL\n");
}
}
}
int prior(char s, char c)
{
if ( c=='^' && s=='+' || s=='-' ||s=='/' || s=='*')
return 1;
else if( c=='*' || c=='/')
{
if(s=='+' || s=='-' )
return 1;
else
return 0;
}
else if( c=='+' || c=='-' )
return 0;
}
void cnvrt(char s[], int n) // convert infix to postfix
{
char g;
int i,j,x;
for(i=0,j=0;i<n;i++)
{
if (s[i]>='0'&&s[i]<='9' || s[i]>='a' && s[i]<='z'|| s[i]>='A' &&
s[i]<='Z')
{
op[j]=s[i];
j++;
}
else if(s[i]=='(')
{
push(s[i]);
}
else if (s[i]=='+' || s[i]=='/' || s[i]=='-' || s[i]=='*' ||
s[i]=='^')
{
if( l1==NULL)
push(s[i]);
else if(l1->data=='(')
push(s[i]);
else if(prior(l1->data, s[i] )!=1)
push(s[i]);
else
{ op[j]=pop();
j++;
push(s[i]);
}
}
else if(s[i]==')')
{
while(l1!=NULL && l1->data!='(')
{
op[j]=pop();
j++;
}
g=pop();
}
}
while(l1!=NULL)
{
op[j]=pop();
j++;
l1=l1->next;
}
}
void main()
{
int i,n;
char c[50];
printf(" enter the no of characters in infix string\n ");
scanf("%d",&n);
printf(" enter the infix string\n");
//for(i=0;i<n;i++)
scanf("%s",c);
cnvrt(c,n);
printf("the postfix string is \n");
for(i=0;i<n;i++)
{
printf("%c",op[i]);
}
}
always one of the operators is missing in the answer..also it gives CORE
DUMPED as output sometimes......... and if infix contains '(' ot ')'
.......then it gives output as stack is empty...... Plz help guys... i am
a student...so ther mi8 b mistakes in my program