关于iterator的程序错误
这段代码在VC里运行为什么会有六个错误呢,应该怎么改啊

#include <vector>
// 引用参数 'occurs ' 可以含有第二个返回值
vector <int> ::const_iterator look_up(
const vector <int> &vec,
int value, // 值在vector 中吗?
int &occurs ) // 多少次?
{
// res_iter 被初始化为最后一个元素的下一位置
vector <int> ::const_iterator res_iter = vec.end();
occurs = 0;
for ( vector <int> ::const_iterator iter = vec.begin();
iter != vec.end();
++iter )
if ( *iter == value )
{
if ( res_iter == vec.end() )
res_iter = iter;
++occurs;
}
return res_iter;
}

错误如下:
error C2143: syntax error : missing '; ' before ' < '
error C2501: 'vector ' : missing storage-class or type specifiers
error C2143: syntax error : missing '; ' before ' < '
error C2039: 'const_iterator ' : is not a member of '`global namespace ' '
error C2143: syntax error : missing '; ' before '{ '
error C2447: missing function header (old-style formal list?)
Error executing cl.exe.

test1.obj - 6 error(s), 0 warning(s)


[解决办法]
using namespace std;
[解决办法]
#include <vector>
using namespace std;