foo.cc: In function 'int main()':
foo.cc:8:12: warning: 'i' is used uninitialized [-Wuninitialized]
    8 |     while(i<n)
      |           ~^~
foo.cc:6:21: note: 'i' was declared here
    6 |         int a=0,b=1,i,c,n;
      |                     ^