View Compilation Error

0_0_32972403_11998.cpp: In function 'int main()':
0_0_32972403_11998.cpp:8:19: error: invalid types 'int[int]' for array subscript
    scanf("%d",&a[i]);
                   ^
0_0_32972403_11998.cpp:16:21: error: '_gcd' was not declared in this scope
    a=a/_gcd(a,arr[i])*arr[i];
                     ^