View Compilation Error

0_0_39312179_18301.cpp: In function 'int main()':
0_0_39312179_18301.cpp:7:9: error: 'f' was not declared in this scope
    7 |         f[0]=f[1]=1;
      |         ^
0_0_39312179_18301.cpp:8:13: error: 'i' was not declared in this scope
    8 |         for(i=2;i<=n;i++){
      |             ^
0_0_39312179_18301.cpp:9:40: error: 'mod' was not declared in this scope
    9 |                 f[i]=(f[i-1]+f[i-2]*2)%mod;
      |                                        ^~~