View Compilation Error

0_0_25336843_12780.cpp: In function 'int main()':
0_0_25336843_12780.cpp:3:11: error: expected initializer before ']' token
  int n,a,b];
           ^
0_0_25336843_12780.cpp:5:2: error: expected initializer before 'f'
  f[1]=1;f[2]=2;
  ^
0_0_25336843_12780.cpp:5:9: error: 'f' was not declared in this scope
  f[1]=1;f[2]=2;
         ^
0_0_25336843_12780.cpp:10:20: error: 'b' was not declared in this scope
   scanf("%d%d",&a,&b);
                    ^