How to read from keyboard a variable number of integers in C++? - c++

Question

I need to read a variable number of integers from keyboard so that I can use each of them.
First I thought I could use something like
int myinteger;
for (int i=0; i<MAX_NUMBER_OF_INTEGERS; i++){
cin >> myinteger;
//What I want to do with that Integer
}
But then I realized that if MAX_NUMBERS_OF_INTEGERS = 10 I have to write 10 integers. But what I want is that I can pass "1 2 3" "1 2 3 4" (for example) and not necessary write 10 integers.

Answer 1

The question seems to have changed a little bit since it was asked and a good answer was given. This just serves to answer the new questions.
#include <iostream>
#include <sstream>
#include <vector>
const int MAX_NUMBERS_OF_INTEGERS = 10;
int main() {
std::string line;
std::cout << "Enter at most " << MAX_NUMBERS_OF_INTEGERS << " ints, separated by spaces: ";
std::getline(std::cin, line);
// create a string stream of the line you entered
std::stringstream ss(line);
// create a container for storing the ints
std::vector<int> myInts;
// a temporary to extract ints from the string stream
int myInteger;
// extract at most MAX_NUMBERS_OF_INTEGERS ints from the string stream
// and store them in the container
while(myInts.size()<MAX_NUMBERS_OF_INTEGERS && ss>>myInteger) myInts.push_back(myInteger);
std::cout << "Extracted " << myInts.size() << " integer(s)\n";
// loop through the container and print all extracted ints.
for(int i : myInts) {
std::cout << i << "\n";
}
// ... or access a certain int by index
if(myInts.size() > 2)
std::cout << "The third int was: " << myInts[2] << "\n";
}

Answer 2

std::vector<int> read_ints;
int _temp;
for(;;)
{
cin >>_temp;
if(!cin.good()) {
break;
}
else {
read_ints.push_back(_temp);
}
}
I haven't tested this solution but it should read an arbitrary number of ints from cin until you enter something else than an integer. You could also skip the saving in the vector part if you don't need to save the results. This is just releveant if you want to save an arbitray number of integers.
EDIT: After clarification your solution could look like this:
int MAX_CHARS = 10;
int my_int;
cin >> setw(MAX_CHARS) >> my_int;
setw limits the number of input characters but you have to include iomanip header
If you want to access every digit, convert int to vector of ints with this function:
vector <int> integerToArray(int x)
{
vector <int> resultArray;
while (true)
{
resultArray.insert(resultArray.begin(), x%10);
x /= 10;
if(x == 0)
return resultArray;
}
}
then you can access each digit with the index e.g. first digit
vectory<int> resultArray = integerToArray(my_int);
int digit = resultArray[0];
Source

Answer 3

One way to read all numbers from a single line limiting them to a maximum number of integers is using std::getline() to get the line into a string then use istringstream in a loop.
#include <iostream>
#include <sstream>
using namespace std;
int main() {
std::string line;
std::getline (std::cin,line);
std::istringstream iss(line);
int myInt;
for(int i=0;(iss >> myInt) && (i < MAX_NUMBER_OF_INTEGERS);++i ) {
std::cout << myInt << ' ';
}
return 0;
}
Note: I did not define MAX_NUMBER_OF_INTEGERS in the code. I could have defined it with const int MAX_NUMBERS_OF_INTEGERS = 10; before usage or possibly that could be a preprocessor define or even a command line parameter. I leave this up to the user.