c++ - 为什么不使用引用地址指针对 C++ 进行编译？

Question

我是一名计算机科学专业的学生，​​正在上我的第一门 C++ 课。我无法理解我的代码发生了什么:

// This program uses the address of each element in the array. 
#include <iostream>
using namespace std;

int main()
{
    const int NUM_COINS = 5;
    int coins[NUM_COINS] = {5, 1, 25, 5, 10};
    int *p1;        // Pointer to a double.
    int count;                      // Counter variable. 

    // Use the pointer to display the values in the array. 
    cout << "Here are the values in the coins array: \n";
    for(count = 0; count << NUM_COINS; count++)
    {
        // Get the address of an array element
        p1 = &coins[count];

        // Display the contents of the element
        cout << *p1;
    }
    cout << endl;
    return 0;
}

1. 所以我的第一个问题是为什么不编译它？我的任何其他简单程序都没有任何问题。我在 OS X 4.2.1 上使用 g++。我必须键入 g++ -o 命令才能编译，如果没有...我会收到以下错误:

g++ -c -o 9-8.o 9-8.cpp cc 9-8.o -o 9-8 Undefined symbols: "std::basic_ostream >& std::operator<<

(std::basic_ostream >&, char const*)", referenced from: _main in 9-8.o _main in 9-8.o "std::ios_base::Init::Init()", referenced from: __static_initialization_and_destruction_0(int, int)in 9-8.o
"std::basic_string, std::allocator >::size() const", referenced from: std::__verify_grouping(char const*, unsigned long, std::basic_string, std::allocator > const&)in 9-8.o "std::basic_string, std::allocator ::operator[](unsigned long) const", referenced from: std::__verify_grouping(char const*, unsigned long, std::basic_string, std::allocator > const&)in 9-8.o std::__verify_grouping(char const*, unsigned long, std::basic_string, std::allocator > const&)in 9-8.o std::__verify_grouping(char const*, unsigned long, std::basic_string, std::allocator > const&)in 9-8.o "___gxx_personality_v0", referenced from: std::__verify_grouping(char const*, unsigned long, std::basic_string, std::allocator > const&)in 9-8.o ___tcf_0 in 9-8.o _main in 9-8.o unsigned long const& std::min(unsigned long const&, unsigned long const&)in 9-8.o __static_initialization_and_destruction_0(int, int)in 9-8.o global constructors keyed to mainin 9-8.o CIE in 9-8.o "std::ios_base::Init::~Init()", referenced from: ___tcf_0 in 9-8.o "std::basic_ostream >& std::endl (std::basic_ostream >&)", referenced from: _main in 9-8.o "std::basic_ostream ::operator<<(std::basic_ostream >& (*)(std::basic_ostream >&))", referenced from: _main in 9-8.o "std::basic_ostream ::operator<<(int)", referenced from: _main in 9-8.o "std::cout", referenced from: _main in 9-8.o _main in 9-8.o _main in 9-8.o ld: symbol(s) not found collect2: ld returned 1 exit status make: *** [9-8] Error 1

这引出了我的第二个问题。即使我确实键入了 g++ 命令，它也会编译，但在运行后会输出一个空数组。所以我的问题 #2 是:我的代码正确吗？如何正确使用带有引用地址语句的指针？

Answer 1

原因:您没有正确使用比较运算符。将其更改为“<”后，您的代码应该可以正常工作。

for(count = 0; count << NUM_COINS; count++)
                     ^ should be "<" here