View Compilation Error

0_0_13792309_22091.cpp: In function 'int main()':
0_0_13792309_22091.cpp:9:17: error: 'sum' was not declared in this scope
         if(sum(a)==b&&sum(b)==a)
                 ^
0_0_13792309_22091.cpp: In function 'int sum(int)':
0_0_13792309_22091.cpp:19:22: error: 'sqrt' was not declared in this scope
     for(i=2;i<=sqrt(x);i++)
                      ^