View Compilation Error

0_0_22802079_19206.cpp: In function 'void get_ans(int)':
0_0_22802079_19206.cpp:16:7: error: 'a' was not declared in this scope
       a[i] = a[i-1] + a[i-3];
       ^
0_0_22802079_19206.cpp: In function 'int main()':
0_0_22802079_19206.cpp:24:13: error: too few arguments to function 'void get_ans(int)'
     get_ans();
             ^
0_0_22802079_19206.cpp:7:6: note: declared here
 void get_ans(int x) {
      ^