Standard Input and Output in C++
Introduction
Standard input and output are fundamental concepts in C++ programming, used for reading data from the user and displaying data to the user. This tutorial will cover the basics of using standard input and output in C++ with detailed explanations and examples.
Basic Output with cout
In C++, the cout object, defined in the iostream header file, is used to output data to the standard output stream, typically the console.
#include <iostream>
using namespace std;
int main() {
cout << "Hello, World!" << endl;
return 0;
}
This code will output:
Basic Input with cin
The cin object, also defined in the iostream header file, is used to read input from the standard input stream, typically the keyboard.
#include <iostream>
using namespace std;
int main() {
int age;
cout << "Enter your age: ";
cin >> age;
cout << "You are " << age << " years old." << endl;
return 0;
}
When you run this code, it will prompt you to enter your age:
You are 25 years old.
Combining cin and cout
You can combine cin and cout to create interactive programs. Here's an example where we read multiple inputs:
#include <iostream>
using namespace std;
int main() {
string name;
int age;
cout << "Enter your name: ";
cin >> name;
cout << "Enter your age: ";
cin >> age;
cout << "Hello, " << name << ". You are " << age << " years old." << endl;
return 0;
}
When you run this code, it will prompt for your name and age:
Enter your age: 30
Hello, Alice. You are 30 years old.
Formatting Output
C++ provides several ways to format output using manipulators like endl, setw, and setprecision from the iomanip header file.
#include <iostream>
#include <iomanip>
using namespace std;
int main() {
double pi = 3.14159;
cout << "Default: " << pi << endl;
cout << "Fixed: " << fixed << pi << endl;
cout << "Set precision: " << setprecision(2) << pi << endl;
return 0;
}
This code will produce the following output:
Fixed: 3.141590
Set precision: 3.14
Error Handling with cin
Handling invalid input is crucial for robust programs. If the user enters invalid input, cin sets an error flag which you can check using cin.fail().
#include <iostream>
using namespace std;
int main() {
int number;
cout << "Enter a number: ";
cin >> number;
if (cin.fail()) {
cout << "Invalid input!" << endl;
} else {
cout << "You entered: " << number << endl;
}
return 0;
}
This code will output an error message if the input is not a valid integer:
Invalid input!
Conclusion
Understanding standard input and output is essential for C++ programming. This tutorial covered the basics of using cout for output, cin for input, formatting output, and handling input errors. Practice these concepts to become proficient in handling input and output in your C++ programs.