Input and Output in C++: Console, Files, and Basic Graphics

1Console input and output

C++ uses cin and cout from the <iostream> library for standard input and output. These are the most basic tools for interacting with the user through the terminal.

How it works:

• cout displays messages or data to the terminal
• cin reads input from the user
• << is the insertion operator (used with cout)
• >> is the extraction operator (used with cin)

Example:

#include <iostream>
using namespace std;

int main() {
    int age;
    cout << "Enter your age: ";
    cin >> age;
    cout << "You entered: " << age << endl;
    return 0;
}

2Inputting multiple values

You can chain cin to read multiple inputs in a single line. The user can enter values separated by spaces or newlines.

int a, b;
cin >> a >> b;
cout << "a = " << a << ", b = " << b << endl;

3Formatting output

C++ provides the <iomanip> library for formatting output. These manipulators give you control over how numbers and text are displayed.

Example – formatting a decimal number:

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

int main() {
    double pi = 3.14159265;
    cout << fixed << setprecision(2) << pi << endl;
    return 0;
}

Example – setting width and alignment:

cout << setw(10) << "Hello" << endl;
cout << left << setw(10) << "World" << endl;

4Reading and writing files

To perform file I/O in C++, include the <fstream> library. This gives you:

• ofstream – for writing to files
• ifstream – for reading from files
• fstream – for both reading and writing

Writing to a file

#include <fstream>
using namespace std;

int main() {
    ofstream outFile("output.txt");
    if (outFile.is_open()) {
        outFile << "Hello, file!" << endl;
        outFile << "This is written using C++." << endl;
        outFile.close();
    }
    return 0;
}

This creates a file named output.txt and writes two lines to it.

Reading from a file

#include <fstream>
#include <iostream>
#include <string>
using namespace std;

int main() {
    ifstream inFile("output.txt");
    string line;

    if (inFile.is_open()) {
        while (getline(inFile, line)) {
            cout << line << endl;
        }
        inFile.close();
    }
    return 0;
}

5File check and error handling

Always check whether a file is open before using it. This prevents crashes and helps you debug issues.

ifstream file("data.txt");
if (!file) {
    cout << "Error opening file." << endl;
    return 1;
}
// Proceed with reading...

6Simple graphics in C++ (intro)

C++ itself does not have built-in graphics. To create graphical applications, you need to use external libraries like:

• SFML – Simple and Fast Multimedia Library
• SDL – Simple DirectMedia Layer
• graphics.h – Older library used with Turbo C++ (mostly legacy)

Here is a simple program using graphics.h (note: this only works in certain environments like Code::Blocks with proper setup):

#include <graphics.h>
int main() {
    int gd = DETECT, gm;
    initgraph(&gd, &gm, "");

    circle(200, 200, 100); // draw circle at x=200, y=200, radius=100
    getch();
    closegraph();
    return 0;
}

7Common mistakes to avoid

8Mini exercises

9Quiz yourself