src.cpp: In function 'int tknp(long long int)':
src.cpp:4:16: error: 'n' was not declared in this scope
int dau=1,cuoi=n,giua=0;
^
src.cpp:6:13: error: 'giua' was not declared in this scope
giua=(dau + cuoi)/2;
^
src.cpp:7:15: error: 'a' was not declared in this scope
if(a[giua]==k){
^
src.cpp:8:14: error: 'dung' was not declared in this scope
dung=1;
^
src.cpp:10:16: error: 'a' was not declared in this scope
if(a[giua] < k){
^