View Compilation Error

855638_0_0_32125.cpp: In function `int main()':
855638_0_0_32125.cpp:6: error: `cin' undeclared (first use this function)
855638_0_0_32125.cpp:6: error: (Each undeclared identifier is reported only once for each function it appears in.)
855638_0_0_32125.cpp:8: error: `(y1 - y2)' cannot be used as a function
855638_0_0_32125.cpp:8: error: `sqrt' undeclared (first use this function)