View Compilation Error

0_0_26153721_24745.cpp: In function 'int main()':
0_0_26153721_24745.cpp:62:19: error: 'MEM' was not declared in this scope
         MEM(tree,0);
                   ^
0_0_26153721_24745.cpp:75:27: error: 'a' was not declared in this scope
             scanf("%d%d",&a,&b);
                           ^
0_0_26153721_24745.cpp:75:30: error: 'b' was not declared in this scope
             scanf("%d%d",&a,&b);
                              ^