View Compilation Error

0_0_6713866_2099.cpp:46: error: `main' must return `int'
0_0_6713866_2099.cpp: In function `int main(...)':
0_0_6713866_2099.cpp:55: error: invalid conversion from `int (*)(grade, grade)' to `int (*)(const void*, const void*)'
0_0_6713866_2099.cpp:55: error:   initializing argument 4 of `void qsort(void*, size_t, size_t, int (*)(const void*, const void*))'
0_0_6713866_2099.cpp:57: error: invalid conversion from `int (*)(grade, grade)' to `int (*)(const void*, const void*)'
0_0_6713866_2099.cpp:57: error:   initializing argument 4 of `void qsort(void*, size_t, size_t, int (*)(const void*, const void*))'
0_0_6713866_2099.cpp:59: error: invalid conversion from `int (*)(grade, grade)' to `int (*)(const void*, const void*)'
0_0_6713866_2099.cpp:59: error:   initializing argument 4 of `void qsort(void*, size_t, size_t, int (*)(const void*, const void*))'