symbol table implementation (user inputs)

//symbol table implementation
#include<stdio.h>
#include<conio.h>
#include<alloc.h>
#include<string.h>
#include<stdlib.h>
#define NULL 0

int size=0;
void Insert();
void Display();
void Delete();
int Search(char lab[]);
void Modify();

struct SymbTab
{
 char label[10],symbol[10];
 int addr;
 struct SymbTab *next;
};
struct SymbTab *first,*last;
void main()
{
 int op,y;
 char la[10];
 clrscr();
 do
 {
  printf("\n\tSYMBOL TABLE IMPLEMENTATION\n");
  printf("\n\t1.INSERT\n\t2.DISPLAY\n\t3.DELETE\n\t4.SEARCH\n\t5.MODIFY\n\t6.END\n");
  printf("\n\tEnter your option : ");
  scanf("%d",&op);
  switch(op)
  {
   case 1:Insert();break;
   case 2:Display();break;
   case 3:Delete();break;
   case 4:printf("\n\tEnter the label to be searched : ");
   scanf("%s",la);
   y=Search(la);
   printf("\n\tSearch Result:");
   if(y==1)
   printf("\n\tThe label is present in the symbol table\n");
   else
   printf("\n\tThe label is not present in the symbol table\n");
   break;
   case 5:Modify();break;
   case 6:exit(0);
  }
 }while(op<6);
 getch();
}

void Insert()
{
 int n;
 char l[10];
 printf("\n\tEnter the label : ");
 scanf("%s",l);
 n=Search(l);
 if(n==1)
 printf("\n\tThe label exists already in the symbol table\n\tDuplicate can’t be inserted");
 else
 {
  struct SymbTab *p;
  p=(struct SymbTab *)malloc(sizeof(struct SymbTab));
  strcpy(p->label,l);
  printf("\n\tEnter the symbol : ");
  scanf("%s",p->symbol);
  printf("\n\tEnter the address : ");
  scanf("%d",&p->addr);
  p->next=NULL;
  if(size==0)
  {
   first=p;
   last=p;
  }
  else
  {
   last->next=p;
   last=p;
  }
  size++;
 }
 printf("\n\tLabel inserted\n");
}

void Display()
{
 int i;
 struct SymbTab *p;
 p=first;
 printf("\n\tLABEL\t\tSYMBOL\t\tADDRESS\n");
 for(i=0;i<size;i++)
 {
  printf("\t%s\t\t%s\t\t%d\n",p->label,p->symbol,p->addr);
  p=p->next;
 }
}

int Search(char lab[])
{
 int i,flag=0;
 struct SymbTab *p;
 p=first;
 for(i=0;i<size;i++)
 {
  if(strcmp(p->label,lab)==0)
  flag=1;
  p=p->next;
 }
 return flag;
}

void Modify()
{
 char l[10],nl[10];
 int add,choice,i,s;
 struct SymbTab *p;
 p=first;
 printf("\n\tWhat do you want to modify?\n");
 printf("\n\t1.Only the label\n\t2.Only the address\n\t3.Both the label and address\n");
 printf("\tEnter your choice : ");
 scanf("%d",&choice);
 switch(choice)
 {
  case 1:
  printf("\n\tEnter the old label : ");
  scanf("%s",l);
  s=Search(l);
  if(s==0)
  printf("\n\tLabel not found\n");
  else
  {
   printf("\n\tEnter the new label : ");
   scanf("%s",nl);
   for(i=0;i<size;i++)
   {
    if(strcmp(p->label,l)==0)
    strcpy(p->label,nl);
    p=p->next;
   }
   printf("\n\tAfter Modification:\n");
   Display();
  }
  break;
  case 2:
  printf("\n\tEnter the label where the address is to be modified : ");
  scanf("%s",l);
  s=Search(l);
  if(s==0)
  printf("\n\tLabel not found\n");
  else
  {
   printf("\n\tEnter the new address : ");
   scanf("%d",&add);
   for(i=0;i<size;i++)
   {
    if(strcmp(p->label,l)==0)
    p->addr=add;
    p=p->next;
   }
   printf("\n\tAfter Modification:\n");
   Display();
  }
  break;
  case 3:
  printf("\n\tEnter the old label : ");
  scanf("%s",l);
  s=Search(l);
  if(s==0)
  printf("\n\tLabel not found\n");
  else
  {
   printf("\n\tEnter the new label : ");
   scanf("%s",nl);
   printf("\n\tEnter the new address : ");
   scanf("%d",&add);
   for(i=0;i<size;i++)
   {
    if(strcmp(p->label,l)==0)
    {
     strcpy(p->label,nl);
     p->addr=add;
    }
    p=p->next;
   }
   printf("\n\tAfter Modification:\n");
   Display();
  }
  break;
 }
}

void Delete()
{
 int a;
 char l[10];
 struct SymbTab *p,*q;
 p=first;
 printf("\n\tEnter the label to be deleted : ");
 scanf("%s",l);
 a=Search(l);
 if(a==0)
 printf("\n\tLabel not found\n");
 else
 {
  if(strcmp(first->label,l)==0)
  first=first->next;
  else if(strcmp(last->label,l)==0)
  {
   q=p->next;
   while(strcmp(q->label,l)!=0)
   {
    p=p->next;
    q=q->next;
   }
   p->next=NULL;
   last=p;
  }
  else
  {
   q=p->next;
   while(strcmp(q->label,l)!=0)
   {
    p=p->next;
    q=q->next;
   }
   p->next=q->next;
  }
  printf("\n\tAfter Deletion:\n");
  Display();
 }
}
//program written by Mars. 7/10/2012. Compiler lab.