C program to make string lower case

#include <stdio.h>
#include<string.h>
int stringlwr(char s[100]);
int main()
{

char str[100];
printf("enter string ");
gets(str);
stringlwr(str);
printf("The string in lower case: %s\n", str);
return 0;
}

int stringlwr(char s[100]){
int i=0;
while(s[i]!='\0'){
if(s[i]>='A' && s[i]<='Z')
s[i]+=32;

i++;
}
return s;
}

Output