C语言strlwr()函数

#include<stdio.h>
#include <string.h>  
int main(){  
  char str[20];  
  printf("Enter string: ");  
  gets(str);//reads string from console  
  printf("String is: %s",str);  
  printf("\nLower String is: %s",strlwr(str));  
 return 0;  
}  

Enter string: lidihuo
String is: lidihuo
Lower String is: lidihuo