foo.cc: In function ‘int main()’:
foo.cc:6:22: warning: ‘a’ is used uninitialized [-Wuninitialized]
    6 |         for(int i=1;i<=a;i++)
      |                     ~^~~
foo.cc:5:13: note: ‘a’ was declared here
    5 |         int a,b=0;
      |             ^