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

By /

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:

ManipulatorUse
setw(n)Sets width of output
setprecision(n)Controls decimal places
fixedUses fixed-point notation
left, rightAligns 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.

Quiz: Input & Output

Question 1/7

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.

Scroll to Top