/in/foo.c: In function 'main':
/in/foo.c:26:16: warning: implicit declaration of function 'Length' [-Wimplicit-function-declaration]
     int cnt1 = Length(s1);
                ^~~~~~
/tmp/ccMxzgYZ.o: In function `main':
foo.c:(.text.startup+0x3f): undefined reference to `Length'
foo.c:(.text.startup+0x4b): undefined reference to `Length'
collect2: error: ld returned 1 exit status