View Compilation Error

0_0_21592091_26873.cpp:1:13: error: expected constructor, destructor, or type conversion before '(' token
         sort(a,a+n);
             ^
0_0_21592091_26873.cpp:2:9: error: 'len' does not name a type
         len=2*a[n-1];///缩小区间
         ^
0_0_21592091_26873.cpp:3:9: error: expected unqualified-id before 'for'
         for(int i=0;i<n;i++)///去掉本身选两次的情况
         ^
0_0_21592091_26873.cpp:3:21: error: 'i' does not name a type
         for(int i=0;i<n;i++)///去掉本身选两次的情况
                     ^
0_0_21592091_26873.cpp:3:25: error: 'i' does not name a type
         for(int i=0;i<n;i++)///去掉本身选两次的情况
                         ^
0_0_21592091_26873.cpp:5:9: error: expected unqualified-id before 'for'
         for(int i=1;i<=len;i++)///选择的无序，除以2
         ^
0_0_21592091_26873.cpp:5:21: error: 'i' does not name a type
         for(int i=1;i<=len;i++)///选择的无序，除以2
                     ^
0_0_21592091_26873.cpp:5:28: error: 'i' does not name a type
         for(int i=1;i<=len;i++)///选择的无序，除以2
                            ^