I am new to C++. I wrote a function in which I want the user to enter an integer value. I know how to prevent the input of characters using:
if(!(cin>>a)) or
if (cin.fail()) where a is of type int. If the user enters characters first and then numbers for eg: ab12 the code works, but if the user inputs the other way round, e.g 12ab, 12 is taken as the input value. How can I prevent that?
Try this:
#include <sstream> #include <string> std::string line; int n; if (std::getline(std::cin, line)) { std::istringstream iss(line); if (iss >> n >> std::ws && iss.get() == EOF) { // success, n is now a valid int } } Or perhaps more usefully in a loop:
for (std::string line; std::getline(std::cin, line); ) { std::istringstream iss(line); if (!(iss >> n >> std::ws && iss.get() == EOF)) { std::cout << "Sorry, did not understand, please try again."; continue; } std::cout << "Thanks. You said: " << n << std::endl; } 