/in/foo.c: In function 'main':
/in/foo.c:27:8: warning: implicit declaration of function 'strcspn' [-Wimplicit-function-declaration]
     s1[strcspn(s1, "\n")] = '\0';
        ^~~~~~~
/in/foo.c:27:8: warning: incompatible implicit declaration of built-in function 'strcspn'
/in/foo.c:27:8: note: include '<string.h>' or provide a declaration of 'strcspn'