foo.cc: In function ‘int main()’:
foo.cc:15:18: warning: ‘r’ may be used uninitialized [-Wmaybe-uninitialized]
   15 |                 r=b1%b2;
      |                 ~^~~~~~
foo.cc:5:15: note: ‘r’ was declared here
    5 |     int a1,b1,r,t,c1,x;
      |               ^