foo.cc: In function ‘int main()’:
foo.cc:7:9: warning: ‘n’ is used uninitialized [-Wuninitialized]
    7 |         if(n==1)
      |         ^~
foo.cc:5:13: note: ‘n’ was declared here
    5 |         int n,a=1,b=1,c,sum=0;
      |             ^