C program to change Upper case to lower case

/*by ankit gehlot
     website:ankitcguru.blogspot.com/
*/


#include<stdio.h>
int main(){
  char str[20];
  int i=0;

  printf("Enter any string :");
  scanf("%s",str);

  while(str[i]!='\0'){
            if(str[i]>=65&&str[i]<=97){
            str[i]=str[i]+32;}i++;
  }
  printf("\nThe string in lowercase is :%s ",str);

  return 0;
}

Output:-

Enter any string :ANKIT
The string in lowercase is :ankit