/in/foo.cc:61:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
 main()
      ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:72:20: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  if((s1.size() ==1)&&(s1[0]==0)||(s2.size() ==1)&&(s2[0]==0))
     ~~~~~~~~~~~~~~~^~~~~~~~~~~~
/in/foo.cc: In function 'void mul(int*, int*, int*)':
/in/foo.cc:45:11: warning: 'k' may be used uninitialized in this function [-Wmaybe-uninitialized]
     c[0]=k+1;
          ~^~