View Compilation Error

0_0_20264861_30164.cpp:7:19: error: conflicting declaration 'int a'
 int a[15],b[15],n,a;
                   ^
0_0_20264861_30164.cpp:7:5: note: previous declaration as 'int a [15]'
 int a[15],b[15],n,a;
     ^
0_0_20264861_30164.cpp: In function 'll work(ll, ll)':
0_0_20264861_30164.cpp:14:18: error: 'gcd' was not declared in this scope
 {return x/gcd(x,y)*y;}
                  ^