View Compilation Error

0_0_21729011_107.cpp: In function 'int main()':
0_0_21729011_107.cpp:30:17: error: 'x2' was not declared in this scope
    f1(x1,i+1)d2(x2,n,n-i){
                 ^
0_0_21729011_107.cpp:30:25: error: 'd2' was not declared in this scope
    f1(x1,i+1)d2(x2,n,n-i){
                         ^