/in/foo.c: In function 'main':
/in/foo.c:17:17: warning: implicit declaration of function 'countChar' [-Wimplicit-function-declaration]
     int count = countChar(str, c);
                 ^~~~~~~~~
/in/foo.c:18:12: warning: too many arguments for format [-Wformat-extra-args]
     printf("两个字符串中小写字母的个数\n", c, count, str);
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/ccx67Ugk.o: In function `main':
foo.c:(.text.startup+0x2c): undefined reference to `countChar'
collect2: error: ld returned 1 exit status