Sentence palindrome

Question

#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main()
{
char str1[100],str2[100];
gets(str1);
for(int i=0;str1[i]!='\0';i++)
{
if(str1[i]>='A'&&str1[i]<='Z')
tolower(str1[i]);
}
strcpy(str2,str1);
strrev(str1);
if(strcmp(str1,str2)==0)
printf("Palindrome!");
else
printf("Not a palindrome");
return 0;
}//please someone find the problem.

Answer 1

use str1 = strrev(str1); because strrev doesnt actually change the content, just return the reversed string. But its not in the c library so I may be talking about another strrev