/in/foo.cc: In function 'int gcd(int, int)':
/in/foo.cc:10:9: warning: 'a' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return a;
         ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:18:4: warning: 'a' may be used uninitialized in this function [-Wmaybe-uninitialized]
   c=gcd(c,m); 
   ~^~~~~~~~~