/in/foo.cc: In function 'int main()':
/in/foo.cc:8:8: warning: unused variable 'a1' [-Wunused-variable]
   char a1[Maxlen],b1[Maxlen];
        ^~
/in/foo.cc:9:23: warning: unused variable 'lena' [-Wunused-variable]
   int a,b[Maxlen]={0},lena,lenb,lenc,x;
                       ^~~~
/in/foo.cc:26:5: warning: 'lenc' may be used uninitialized in this function [-Wmaybe-uninitialized]
    x=b[lenc];
    ~^~~~~~~~