Learn C++ Programming

Basic Input with cin

#include <iostream>
using namespace std;

int main() {
  int number;
  cout << "Enter a number: ";
  cin >> number;
  cout << "You entered: " << number;
  return 0;
}

How it works:

cin reads input until whitespace (space, tab, newline)
The extraction operator >> converts input to the variable type
Program waits at cin until user presses Enter

Multiple Inputs

Chained Input

int age;
double height;
cout << "Enter age and height: ";
cin >> age >> height;

Input with Prompt

cout << "Enter age: ";
cin >> age;
cout << "Enter height: ";
cin >> height;

String Input

#include <string>

string name;
cout << "Enter your name: ";
cin >> name;  // Stops at first whitespace

string fullName;
cout << "Enter full name: ";
cin.ignore();  // Clear input buffer
getline(cin, fullName);  // Reads entire line

Key Differences:

Method	Behavior	When to Use
`cin >> var`	Stops at whitespace	Single words/simple input
`getline(cin, var)`	Reads entire line	Strings with spaces/multi-word input

Input Validation

int age;
while (true) {
  cout << "Enter age (1-120): ";
  if (cin >> age && age >= 1 && age <= 120) {
    break;
  }
  cout << "Invalid input!\n";
  cin.clear();  // Clear error state
  cin.ignore(1000, '\n');  // Discard bad input
}

Validation Techniques:

Check stream state with cin.fail()
Clear errors with cin.clear()
Discard bad input with cin.ignore()
Range checking for numeric values

Common Pitfalls

Mixing cin >> and getline():

cin.ignore(); // Required after cin >>before getline

No input validation: Users may enter wrong data types

Buffer overflow: When reading into fixed-size arrays

char name[20]; cin.getline(name, 20); // Safer than gets()

Advanced Techniques

Character Input

char ch;
cout << "Press a key: ";
ch = cin.get();  // Gets single character

cin.get(ch);    // Alternative method

File-like Input

string line;
while (getline(cin, line)) {
  if (line.empty()) break;
  cout << "Read: " << line << endl;
}