View Compilation Error

0_0_24416602_25972.cpp: In function 'int main()':
0_0_24416602_25972.cpp:15:13: error: 'i' was not declared in this scope
         for(i = 0;i < n;i ++)  
             ^
0_0_24416602_25972.cpp:18:14: error: 'a' was not declared in this scope
         sort(a,a+n,compare);  
              ^
0_0_24416602_25972.cpp:20:13: error: 'i' was not declared in this scope
         for(i = 0;i < n;i ++){  
             ^