How to Input Multiple Integer Using CIN C++

[jasonson]

How do I input 1 integer A and input multiple integer based on the number of integer A in one line using cin?

example input:
3 3 1 2 (the first input is 3, so I want to input 3 variables)
2 7 8 (the first input is 2, so I want to input 2 variables)
4 5 3 7 2 (the first input is 4, so I want to input 4 variables)

[laserlight]

It sounds like it would be appropriate to use nested loops: the outer loop loops over each line of input, reading the first number of each line and then going into the inner loop; the inner loop loops as many times as the first number of the line, hence reading the remaining input on the line.

[LMHmedchem]

If you use cin to dump your input to a string, you can then parse the string on your delimiter (in this case space) into a vector and then manipulate the resulting vector however you need to. If you are programming in c++, you may as well use containers.

In this case, the first element of the vector would contain the number of variables and the rest of the vector would contain the variable values.

#include <iostream>
#include <string>
#include <sstream>

int main() {

   // declare string to hold input and initialize to blank
   string input_string;  input_string.assign("");

   cout << endl;
   cout << "input space delimited series of integers" << endl;
   cout << endl;

   // read input from standard in
   cin >> input_string;

   cout << endl;
   cout << "processing input:" << endl;
   cout << input_string << endl;
   cout << endl;

   // to parse input string
   stringstream input_parser_stream;

   //load row string to stringstream
   input_parser_stream << input_string;

   // temp string to hold each parsed cell value
   string input_element;  input_element.assign("");

   // input delimiter
   string input_delimiter;  input_delimiter.assign(' ');

   // vector to hold parsed input
   vector<string> parsed_input;

   // parse input string into elements on delimiter
   while(getline(input_parser_stream, input_element, input_delimiter)) {

      // remove '\r' EOL chars
      input_element.erase(remove(input_element.begin(),input_element.end(),'\r') , input_element.end());

      // add parsed element to vector
      parsed_input.push_back(input_element);

      // reinitialize element string
      input_element.assign("");
   }

   // clear the buffer
   input_stream.clear();

   // print input
   cout << endl;
   cout << "line: " << input_string << endl;
   // first element of parsed_input[] contains the number of input variables
   cout << "has " << parsed_input[0] << "  variables" << endl;
   // print all elements after the first
   for(unsigned int i=1; i<parsed_input.size(); i++) { cout << parsed_input[i] << endl; }
   cout << endl;

   // clear the parsed input vector for next use
   parsed_input.clear();

// int main() endbrace
}

There isn't any need to evaluate the number of inputs if you implement something similar to this. If you were going to evaluate multiple strings, you would put the cin statement into a loop and it would be best to create a separate function to process each input string.

Keep in mind that how you store any data is related to how you need to retrieve it later so that is something you need to think about sooner rather than later.

Note 1: The values in parsed_input[] are stored as standard strings, so if you need to use them as integers (such as to do math), you will need to do a type conversion at some point. That would probably be best to do before you push each parsed element into the vector. If you need ints in the end, use a vector of int and convert each element string to int using something like stoi() before pushing it.

// vector to hold parsed input
vector<int> parsed_input;
// convert from string to int and add parsed element to vector
parsed_input.push_back( atoi( input_element.c_str() ) );

Note 2: I did not compile the above, so there could be an issue here or there. Let me know if what I posted isn't clear.

LMHmedchem

[2kaud]

// read input from standard in
cin >> input_string;

This will only extract data from cin until the first white-space char following non-white space chars. So if the input is
3 3 1 2

then only the first 3 will be extracted to input_string. Consider

#include <iostream>
#include <string>
#include <sstream>
#include <vector>
using namespace std;

int main()
{
	const char input_delimiter = ' ';

	string input_string;

	cout << "Input space delimited series of integers" << endl;
	getline(cin, input_string);

	stringstream input_parser_stream (input_string);
	vector<string> parsed_input;

	for (string input_element; getline(input_parser_stream, input_element, input_delimiter); parsed_input.push_back(input_element));

	cout << "The values are" << endl;

	for (const auto& p : parsed_input)
		cout << p << endl;

	cout << endl;
}

This has the issue, however, that irrespective of the value of the first integer entered, all the data values entered will be parsed and stored. Doing it this way doesn't really require an initial count of numbers to be read.

Based upon lasrlight's post #2, consider

#include <iostream>
#include <vector>
using namespace std;

int main()
{
	int num;
	vector<int> vi;

	cout << "Input space delimited series of integers" << endl;
	cin >> num;

	for (int n = 0; n < num; ++n) {
		int val;
		cin >> val;
		vi.push_back(val);
	}

	cout << "\nThe numbers are" << endl;

	for (const auto& v : vi)
		cout << v << endl;

	cout << endl;
}