View Compilation Error

0_0_25247364_4838.cpp: In function 'int main()':
0_0_25247364_4838.cpp:62:24: error: 'a' was not declared in this scope
     tmp = make_pair(xx[a]+dx[k], yy[a]+dy[k]);   
                        ^
0_0_25247364_4838.cpp:73:24: error: 'a' was not declared in this scope
     tmp = make_pair(xx[a]+dx[k], yy[a]+dy[k]);   
                        ^