/in/isSibling.c: In function 'sort':
/in/isSibling.c:8:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (i = 0; i < strlen(s) - 1; i++)
                   ^
/in/isSibling.c:10:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (j = 0; j < strlen(s) - 1 - i; j++)
                       ^
/in/isSibling.c: In function 'main':
/in/isSibling.c:27:5: warning: implicit declaration of function 'gets_s'; did you mean 'fgetpos'? [-Wimplicit-function-declaration]
     gets_s(s1);
     ^~~~~~
     fgetpos
/tmp/cctqOg0j.o: In function `main':
ex4.c:(.text+0x0): multiple definition of `main'
/tmp/ccMS5lcQ.o:isSibling.c:(.text+0x11b): first defined here
/tmp/ccMS5lcQ.o: In function `main':
isSibling.c:(.text+0x145): undefined reference to `gets_s'
isSibling.c:(.text+0x159): undefined reference to `gets_s'
/tmp/cctqOg0j.o: In function `main':
ex4.c:(.text+0xa1): undefined reference to `isSibling'
collect2: error: ld returned 1 exit status