View Compilation Error

0_0_38243378_20531.cpp: In function 'int main()':
0_0_38243378_20531.cpp:18:28: error: 'prime_number' was not declared in this scope
    if(value==prime_number(n)){
                            ^
0_0_38243378_20531.cpp: In function 'int prime_number(int)':
0_0_38243378_20531.cpp:33:16: error: 'sqrt' was not declared in this scope
  int num=sqrt(i);
                ^