Use of strtok in C

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

#define CSE 100

char str1[CSE],str2[CSE],str3[CSE];

int main()
{
long len,i,cs=1;

char *ptr;

while(i)
{
    gets(str1);
ptr = strtok (str1," ");

while(ptr!=NULL)
{
      //printf("CASE  %ld : %s\n",cs++,ptr);
strcpy(str2,ptr);
  printf("CASE  %ld : %s\n",cs++,str2);
  ptr = strtok (NULL, " ");
 
  memset(str2,'\0',sizeof(str2));
}
}

return 0;
}