View Compilation Error

0_0_38585444_28622.cpp: In function 'int prime(int)':
0_0_38585444_28622.cpp:19:14: error: 'sqrt' was not declared in this scope
     k = (int)sqrt(n+1);
              ^~~~
0_0_38585444_28622.cpp:19:14: note: suggested alternative: 'qsort'
     k = (int)sqrt(n+1);
              ^~~~
              qsort