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

What You’ll Learn

By the end of this post, you will:

• Use cin and cout for console input/output
• Format output using manipulators
• Read from and write to text files
• Understand how to use simple graphics libraries (intro only)

---

Console Input and Output

C++ uses cin and cout from the <iostream> library for standard input and output.

Example:

#include <iostream>
using namespace std;

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

How it works:

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

---

Inputting Multiple Values

You can chain cin to read multiple inputs:

int a, b;
cin >> a >> b;

If the user types 5 10, a becomes 5 and b becomes 10.

---

Formatting Output

C++ provides the <iomanip> library to format output.

Common manipulators:

Manipulator	Use
setw(n)	Sets width of output
setprecision(n)	Controls decimal places
fixed	Uses fixed-point notation
left, right	Aligns text

Example:

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

int main() {
    double pi = 3.14159265;
    cout << fixed << setprecision(2) << pi << endl;  // Output: 3.14
    return 0;
}

---

Reading and Writing Files

To use file I/O in C++, include the <fstream> library.

Step 1: Include the header

#include <fstream>

Step 2: Declare file streams

• Use ofstream for writing to files
• Use ifstream for reading from files

---

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 will create a file named output.txt and write 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;
}

This program reads output.txt line by line and prints it to the console.

---

File Check and Error Handling

Always check whether a file is open before using it.

ifstream file("data.txt");
if (!file) {
    cout << "Error opening file." << endl;
}

---

Simple Graphics in C++ (Intro)

C++ itself doesn’t have built-in graphics, but you can use external libraries like:

• SFML
• SDL
• graphics.h (older, Turbo C++ style)

Here’s a simple program using graphics.h (only works in some environments like Code::Blocks with 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;
}

This displays a simple window with a circle. Graphics programming requires proper setup, which we’ll cover later in a dedicated post.

---

Mini Exercises

1. Ask the user to enter their name and age, and print a message like:
   Hello Sarah, you are 21 years old.
2. Create a program that writes 5 numbers to a file, one per line.
3. Write a program to read numbers from a file and print their sum.

---

Common Mistakes to Avoid

• Forgetting to include headers like <fstream> or <iomanip>
• Not checking if a file was successfully opened
• Missing cin.ignore() when mixing cin and getline()
• Trying to use graphics without setting up the required environment

---

Summary

In this post, you learned:

• How to use cin and cout for user interaction
• How to format output with manipulators
• How to perform file input/output in C++
• Basic concepts of using graphics in C++

---

What’s Next?

In the next post, we’ll explore Functions in C++ — including parameters, return values, and how to structure your code using reusable logic blocks.