View Compilation Error

0_0_21107168_19403.cpp:24:8: error: 'MAXN' was not declared in this scope
 node a[MAXN];  
        ^
0_0_21107168_19403.cpp:30:16: error: 'MAXN' was not declared in this scope
 vector <int> G[MAXN];  
                ^
0_0_21107168_19403.cpp: In function 'int main()':
0_0_21107168_19403.cpp:40:13: error: 'G' was not declared in this scope
             G[i].clear();  
             ^
0_0_21107168_19403.cpp:42:25: error: 'a' was not declared in this scope
             scanf("%d",&a[i].cnt);  
                         ^
0_0_21107168_19403.cpp:45:14: error: 'a' was not declared in this scope
         sort(a+1,a+n+1,cmp);  
              ^
0_0_21107168_19403.cpp:56:21: error: 'G' was not declared in this scope
                     G[a[i].ID].push_back(a[j].ID);  
                     ^
0_0_21107168_19403.cpp:62:16: error: 'G' was not declared in this scope
             if(G[a[i].ID].size()<a[i].cnt){  
                ^
0_0_21107168_19403.cpp:74:27: error: 'G' was not declared in this scope
             for(int j=0;j<G[i].size();j++){  
                           ^