View Compilation Error

0_0_6002414_10389.cpp: In function `double caldis(Point, Point)':
0_0_6002414_10389.cpp:15: error: `sqrt' undeclared (first use this function)
0_0_6002414_10389.cpp:15: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_6002414_10389.cpp: In function `int cmp(Point, Point)':
0_0_6002414_10389.cpp:20: error: `a' undeclared (first use this function)
0_0_6002414_10389.cpp: At global scope:
0_0_6002414_10389.cpp:24: error: `Point a' used prior to declaration
0_0_6002414_10389.cpp: In function `int main()':
0_0_6002414_10389.cpp:33: error: `cin' undeclared (first use this function)
0_0_6002414_10389.cpp:45: error: `sort' undeclared (first use this function)
0_0_6002414_10389.cpp:55: error: expected `;' before '}' token
0_0_6002414_10389.cpp:63: error: `cout' undeclared (first use this function)
0_0_6002414_10389.cpp:63: error: `endl' undeclared (first use this function)