For循环使用getline在vector中输入字符串

Question

So I have an assignment for school, I need to declare a vector of strings then use a for loop to input names into the vector using get line. This code is what I have so far, I was trying to make a variable for a location in my vector, then input a string into the vector based on the value of my variable. Im using C++.

What Im wondering is: whats the flaw in my logic?

#include "stdafx.h"
#include <iostream>;
#include <vector>;
#include <string>;
using namespace std;


int _tmain(int argc, _TCHAR* argv[])
{
vector<string> name_list(10);
int n;
for (name_list[n]; cin.getline >> name_list[n]; ++n)
    cin >> name_list[n];
cout << name_list[n];
int stop; cin >> stop;
return 0;
}

EDIT::: So I figured it out! Thank you 0x499602D2, You kinda set me on the right way. the code I came up with is this::

int _tmain(int argc, _TCHAR* argv[])
{
vector<string> name_list(11);
int n = 0;
for (int n = 0; n < 11; ++n);
getline(cin, name_list[n]);
cout << name_list[n];

int stop; cin >> stop;
return 0;
}

Answer 1

Not only is n uninitialized, you're also doing cin.getline >> name_list[n] which shouldn't even compile as far as I know. getline is a member function of std::cin that reads a line from input into a character array. It's not needed here as we are trying to read into a vector.

Moreover, since you want to get names from the user input into each slot in the vector, attempting to retrieve a line with getline also wouldn't make sense.

n needs to be initialized to an integer that when access with name_list[n] , will give us the start of the vector (that would be 0 ), and instead of getline , we use the operator >> to get each whitespace separated input. Like this:

for (int n = 0; std::cin >> name_list[n]; ++n)
    ; // empty

A statement isn't needed within the for loop body as its already been done in the loop parameters.

---

Another thing you need to look out for is overrunning the size of the vector. You initialized name_list with a size of 10 , and if the user enters in, say, 11 names, accessing an index with name_list[n] will cause Undefined Behavior in your program, which is a special way of saying your program will be invalid.

It's better to use the at() member function as it will throw an exception if you try to access an out-of-bounds address:

for (int n = 0; std::cin >> name_list.at(n); ++n)
//                                   ^^^^^^
    ;

Answer 2

您需要初始化n = 0，在第二个for参数中，您可能想将cin移入循环并用i <10替换它，因为否则循环将不知道何时停止