Write a c program to check given string is palindrome number or not

#include<string.h>

#include<stdio.h>

int main(){

  char *str,*rev;

  int i,j;

  printf("\nEnter a string:");

  scanf("%s",str);

  for(i=strlen(str)-1,j=0;i>=0;i--,j++)

      rev[j]=str[i];

      rev[j]='\0';

  if(strcmp(rev,str))

      printf("\nThe string is not a palindrome");

  else

      printf("\nThe string is a palindrome");

  return 0;

}