View Compilation Error

0_0_29181700_30734.cpp:1:7: error: 'MAIN' was not declared in this scope
 int a[MAIN]={},len=1;
       ^
0_0_29181700_30734.cpp:2:8: error: expected constructor, destructor, or type conversion before '(' token
  memset(a,0,sizeof(a));
        ^
0_0_29181700_30734.cpp:3:2: error: 'a' does not name a type
  a[0]=1; 
  ^
0_0_29181700_30734.cpp:4:2: error: expected unqualified-id before 'for'
  for(int j=2;j<=n;j++){
  ^
0_0_29181700_30734.cpp:4:14: error: 'j' does not name a type
  for(int j=2;j<=n;j++){
              ^
0_0_29181700_30734.cpp:4:19: error: 'j' does not name a type
  for(int j=2;j<=n;j++){
                   ^
0_0_29181700_30734.cpp:14:2: error: expected unqualified-id before 'for'
  for(int i=len-1;i>=0;i--)
  ^
0_0_29181700_30734.cpp:14:18: error: 'i' does not name a type
  for(int i=len-1;i>=0;i--)
                  ^
0_0_29181700_30734.cpp:14:23: error: 'i' does not name a type
  for(int i=len-1;i>=0;i--)
                       ^