foo.cc: In function 'bool prime(int)':
foo.cc:7:20: error: 'sqrt' was not declared in this scope
     for(int i=2;i<=sqrt(x);i++) if(x%i==0) return false;
                    ^~~~
foo.cc:7:20: note: suggested alternative: 'qsort'
     for(int i=2;i<=sqrt(x);i++) if(x%i==0) return false;
                    ^~~~
                    qsort
foo.cc: In function 'int main()':
foo.cc:20:20: error: 'sqrt' was not declared in this scope
     for(int i=2;i<=sqrt(n);i++) 
                    ^~~~
foo.cc:20:20: note: suggested alternative: 'qsort'
     for(int i=2;i<=sqrt(n);i++) 
                    ^~~~
                    qsort

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