/in/foo.c: In function 'test':
/in/foo.c:9:5: warning: implicit declaration of function 'strrev' [-Wimplicit-function-declaration]
     strrev(x);
     ^~~~~~
/in/foo.c: In function 'main':
/in/foo.c:22:22: warning: format '%s' expects argument of type 'char *', but argument 2 has type 'int' [-Wformat=]
             printf("%s\n",strrev(mw[i]));
                      ^
/tmp/ccR9Tj67.o: In function `test':
foo.c:(.text+0x3e): undefined reference to `strrev'
/tmp/ccR9Tj67.o: In function `main':
foo.c:(.text.startup+0xaf): undefined reference to `strrev'
collect2: error: ld returned 1 exit status