Tokens - Separating Identifier Keyword Condition Punctuators Branching Controls in C

#include<stdio.h>
#include<conio.h>
#include<string.h>
int key=0;
char expr[100];
char cont[][20]={"CONTROLS","for","do","while","NULL"};
char cond[][20]={"CONDITIONS","if","else","elseif","NULL"};
char optr[][20]={"OPERATOR","+","-","*","/","%","<",">","<=",">=","=","(",")","NULL"};
char branch[][20]={"BRANCHING","goto","jump","NULL"};
void checking(char[],char[][20]);
void main()
{
 int i,j,k,l,m,n,c,c1;
 char sbexpr[50],txt[3];
 clrscr();
 printf("enter the expression:");
 gets(expr);
 for(i=0;expr[i]!=NULL;i++)
 {
  key=0;
  for(j=i,k=0;expr[i]!=32 && expr[i]!=NULL;i++,j++,k++)
   sbexpr[k]=expr[j];
  sbexpr[k]=NULL;
  if(key==0)
   checking(sbexpr,cond);
  if(key==0)
   checking(sbexpr,cont);
  if(key==0)
   checking(sbexpr,branch);
  if(key==0)
   checking(sbexpr,optr);
  if(key==0)
  {
   c=0;c1=0;
   for(m=0;sbexpr[m]!=NULL;m++)
   {
    key=0;
    if((key==0) || ((sbexpr[m]>97 && sbexpr[m]<=122) || (sbexpr[m]>=65 && sbexpr[m]<=90)|| (sbexpr[m]>=48 && sbexpr[m]<=57)))
    {
     c++;
     if(sbexpr[m]>=48 && sbexpr[m]<=57)
      c1++;
     key=1;
    }
   }
   if(c1==c)
     printf("%s\t--------> Identifier(It is a numerical value)\n",sbexpr);
   else if(m==c)
     printf("%s\t--------> Identifier\n",sbexpr);
   else
     printf("%s\t--------> Invalid Symbol\n",sbexpr);
   key=1;
  }
  if(key==0)
  {
   printf("%s\t----------->    Address\n",sbexpr);
   key=1;
  }
 }
 getch();
}
void checking(char expr[],char check[][20])
{
 int i;
 for(i=1;strcmp(check[i],"NULL")!=0;i++)
 {
  if(strcmp(expr,check[i])==0)
  {
   printf("%s\t--------> %s\n",expr,check[0]);
   key=1;
   break;
  }
 }
}