If a string is rotation of other. All test cases Not running - c

Question

I am using the logic of concatenation the 2nd string and then searching first string in it.
But for some reason, the code does not run for all test cases.
example
s1 = rahul , s2 = hulra
s2.s2 = hulrahulra
and then search s1 in s2.s2 using strstr() function.
#include <stdio.h>
#include <string.h>
int ifRotation(char *s1, char *s2)
{
int l1 = strlen(s1);
int l2 = strlen(s2);
char str1[l1], str2[l2+ l2];
int i;
i = 0;
while(*s1 != '\0')
{
str1[i] = *s1;
i++;
s1++;
}
i = 0;
while(*s2 != '\0')
{
str2[i] = *s2;
i++;
s2++;
}
strcat(s2, s2);
if(strstr(s2, s1))
{
return 1;
}
return 0;
}
int main() {
//code
int queries;
scanf("%d", &queries);
int array[queries];
char str1[100];
char str2[100];
int i = 0;
while(i < queries)
{
scanf("%s", &str1);
scanf("%s", &str2);
array[i] = ifRotation(str1, str2);
i++;
}
i = 0;
while(i < queries)
{
printf("%d\n", array[i]);
i++;
}
return 0;
}
Please tell me what's wrong with the code?

Answer 1

You are just copying from one string to another, and the copy routine has several problems.
char str1[l1] is not large enough. It should be char str1[l1 + 1]. The extra 1 is for the null character.
The string should always end with null character '\0'.
s1 and s2 are incremented until they reach the null character, so by that time s1 and s2 are empty.
Try the following code for copying the strings, you will see s1/s2 will be empty, str1/str2 are just copies of the original s1/s2.
You can fix the copying as follows:
char str1[l1 + 1], str2[l2 + 1];
int i;
i = 0;
while(*s1 != '\0')
{
str1[i] = *s1;
i++;
s1++;
}
str1[i] = '\0';
i = 0;
while(*s2 != '\0')
{
str2[i] = *s2;
i++;
s2++;
}
str2[i] = '\0';
printf("s1=%s, s2=%s, str1=%s, str2=%s\n", s1, s2, str1, str2);
//output: s1=, s2=, str1=old_s1, str2=old_s2
But this doesn't really achieve anything. If you just want to check "rahul" is the reverse of "hulra", keep s1 as it is, copy s2 to reverse_s2 in reverse order, and compare the two strings as follows:
#include <stdio.h>
#include <string.h>
int ifRotation(const char *s1, const char *s2)
{
if(!s1 || !s2)
return 0;
int len2 = strlen(s2);
char reverse_s2[len2 + 1];
//copy s2 to reverse_s2 in reverse order:
int i = 0;
for(i = 0; i < len2; i++)
reverse_s2[i] = s2[len2 - i - 1];
reverse_s2[i] = '\0'; //add null character
int result = strcmp(s1, reverse_s2) == 0;
return result;
}
int main(void)
{
printf("%d\n", ifRotation("rahul", "hulra"));
printf("%d\n", ifRotation("rahul", "luhar"));
return 0;
}