View Compilation Error

222613_0_30774.cpp: In function `float fac(float)':
222613_0_30774.cpp:15: error: `sqrt' undeclared (first use this function)
222613_0_30774.cpp:15: error: (Each undeclared identifier is reported only once for each function it appears in.)
222613_0_30774.cpp:16: error: cannot convert `float (*)(float)' to `float' in return