View Compilation Error

0_0_2046353_30789.cpp: In function `int main()':
0_0_2046353_30789.cpp:21: error: `memset' undeclared (first use this function)
0_0_2046353_30789.cpp:21: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_2046353_30789.cpp:22: error: `cin' undeclared (first use this function)
0_0_2046353_30789.cpp:25: error: `x2' undeclared (first use this function)
0_0_2046353_30789.cpp:25: error: `y2' undeclared (first use this function)
0_0_2046353_30789.cpp:26: error: `x1' undeclared (first use this function)
0_0_2046353_30789.cpp:26: error: `y1' undeclared (first use this function)
0_0_2046353_30789.cpp:26: error: `num' undeclared (first use this function)
0_0_2046353_30789.cpp:31: error: `cout' undeclared (first use this function)
0_0_2046353_30789.cpp:31: error: `i' undeclared (first use this function)
0_0_2046353_30789.cpp:31: error: `j' undeclared (first use this function)