foo.c: In function 'main':
foo.c:7:15: error: 'k1' undeclared (first use in this function)
    7 |         for(i=k1;i<=k2;i++){
      |               ^~
foo.c:7:15: note: each undeclared identifier is reported only once for each function it appears in
foo.c:7:21: error: 'k2' undeclared (first use in this function)
    7 |         for(i=k1;i<=k2;i++){
      |                     ^~

[Hydro](https://hydro.ac)提供评测服务