Input and output: std::cout, std::cin, streams

Worked example

Read it before you run it

#include <iostream>
// Header that provides std::cout, std::cin and std::cerr.
#include <sstream>
// Header for std::istringstream, a stream that reads from a string.
double target{};
// Variable to receive the target angle (value-initialized to 0.0).
std::cout << "Target angle (deg): ";
// Print a prompt without a newline.
if (!(std::cin >> target)) {
// Try to read a number; the condition is true when reading failed.
  std::cerr << "not a number\n";
// Report the problem on the error stream.
  return 1;
// Leave main with a non-zero exit code, meaning failure.
}
// End of the failure branch.
std::istringstream line{"12.5 3"};
// A stream that reads from a string, handy for parsing and for tests.
int joint{}; double speed{}; line >> speed >> joint;
// Extract two values in order; a stream parses text into typed values.

Practice code

Now type it yourself

Copy the starter into practice.cpp and replace every TODO with your own code. Build and run it: g++ -std=c++17 -Wall -Wextra -Wpedantic practice.cpp -o practice -pthread && ./practice

#include <iostream>
#include <sstream>

int main() {
  std::istringstream line{"12.5 3"};  // pretend this text was typed by a user
  double speed{};
  int joint{};
  // TODO: read speed then joint from line; if reading fails print "bad input" to std::cerr and return 1
  std::cout << "joint " << joint << " speed " << speed << '\n';
  return 0;
}

joint 3 speed 12.5

#include <iostream>
#include <sstream>

int main() {
  std::istringstream line{"12.5 3"};  // pretend this text was typed by a user
  double speed{};
  int joint{};
  if (!(line >> speed >> joint)) {
    std::cerr << "bad input\n";
    return 1;
  }
  std::cout << "joint " << joint << " speed " << speed << '\n';
  return 0;
}