我需要根据从早期输入确定的可修改数量的变量来获取输入。
如果您在早期函数中获得的输入为1，则代码将类似于
std::string istring;
std::getline(std::cin, istring);
std::istringstream stream(istring);
while (stream >> a)
{
statement;
}
是否可以为while循环创建一个条件，该条件会根据您的输入而变化？因此，如果输入是例如5，它将表现得像
while (stream >> a >> a >> a >> a >> a)
{
statement;
}
我尝试过while ((stream>>a)*number)，但这不起作用
答案 0 :(得分：3)
首先回答您的具体问题：
我需要根据从早期输入中确定的可修改数量的变量来获取输入。
C ++中的解决方案是istringstream，while循环和vector的组合：
#include <iostream>
#include <string>
#include <sstream>
#include <vector>
int main() {
unsigned int earlierInput = 5; // this is the earlier input
std::vector<int> numbers; // The type of vector also controls what
// data type you want the user to give
// you. Because the stream will try to
// the user input into that type.
while (numbers.size() != earlierInput) {
// Here we ask the user for input and convert the input
// to a stream, like that we can try to convert the user
// input into the data type we want.
std::string istring;
std::cout << "Please type in " << earlierInput << " numbers: ";
std::getline(std::cin, istring);
std::istringstream reader(istring);
// read as many numbers as possible.
for (int number; reader >> number;) {
numbers.push_back(number);
}
if (numbers.size() != earlierInput) {
// if not enough numbers empty vector and print
// error message
std::cout << "Not the right amount of numbers!";
std::cout << "Try again!" << std::endl;
numbers.clear();
}
}
// If we get here the user typed in the right amount of numbers
std::cout << "You typed the following numbers:" << std::endl;
for (const int& i : numbers) {
std::cout << i << std::endl;
}
}
这仅适用于一个用户输入。如果你想要用户任意一次这样做（例如你想要用户10次询问5个号码），那么你需要再次应用上面的规则，然后叠加：
#include <iostream>
#include <string>
#include <sstream>
#include <vector>
int main() {
unsigned int amountOfInputs = 2; // this is the amount of times
// you want the user to type
// something in
unsigned int earlierInput = 5; // this is the earlier input
std::vector<std::vector<int>> allNumbers; // Now we need a vector in
// a vector to store the results.
// The type of the inner vector also
// controls what data type you want the
// user to give you.
while (allNumbers.size() != amountOfInputs) {
std::vector<int> numbers; // This is the vector as in the example
// above.
while (numbers.size() != earlierInput) {
// Here we ask the user for input and convert the input
// to a stream, like that we can try to convert the user
// input into the data type we want.
std::string istring;
std::cout << "Please type in " << earlierInput << " numbers: ";
std::getline(std::cin, istring);
std::istringstream reader(istring);
// read as many numbers as possible.
for (int number; reader >> number;) {
numbers.push_back(number);
}
if (numbers.size() != earlierInput) {
// if not enough numbers empty vector and print
// error message
std::cout << "Not the right amount of numbers!";
std::cout << "Try again!" << std::endl;
numbers.clear();
}
}
// If we get here the user typed in the right amount of numbers
// and we can save them and clear the array for using it again.
allNumbers.push_back(numbers);
numbers.clear();
}
std::cout << "You typed the following numbers:" << std::endl;
unsigned int round = 1;
for (auto numbersOfRound : allNumbers) {
std::cout << "For round " << round++ << ": ";
for (auto i: numbersOfRound) {
std::cout << i;
}
std::cout << std::endl;
}
}
要保存任意数量的数据并能够访问它，您必须使用动态分配的数组或类似的任何内容。这是因为在编译时你不知道在运行时需要多少变量，因此你不能给它们全部命名。
理论上，流可能是无限长字符串或数据（另请参阅here）。因此，用户输入stream，因为它理论上可能是无限长的。虽然这不适用于实践。
要从流中提取信息，必须使用>>运算符，也称为提取运算符。此运算符不支持vectors作为（rhs）操作数，如文档here中所述。它仅支持基本数据类型（这就是我们在上面的示例中需要临时变量int number的原因）。