View Compilation Error

0_0_31553340_22522.cpp: In function 'int main()':
0_0_31553340_22522.cpp:8:16: error: 'x2' has not been declared
  ll  f1(int x1,x2);
                ^
0_0_31553340_22522.cpp:15:3: error: expected ';' before 'if'
   if(z==1)sum=1;
   ^
0_0_31553340_22522.cpp: At global scope:
0_0_31553340_22522.cpp:23:14: error: 'x2' has not been declared
 ll f1(int x1,x2)
              ^
0_0_31553340_22522.cpp: In function 'long long int f1(int, int)':
0_0_31553340_22522.cpp:29:15: error: 'x2' was not declared in this scope
  for( i=4; i<(x2-x1); i++)
               ^