C++ File handling: Calculate average of numbers in a file

Last update on April 14 2025 12:45:11 (UTC/GMT +8 hours)

15. Calculate the Average of Numbers Stored in a File

Write a C++ program to calculate the average of numbers stored in a file.

Sample Solution:

C Code:

#include <iostream>   // Including the input/output stream library
#include <fstream>    // Including the file stream library
#include <string>     // Including the string handling library

// Function to display the content of a file
void displayFileContent(const std::string &filename) {
  std::ifstream file(filename); // Open file with given filename for reading
  std::string line; // String to store each line of the file

  if (file.is_open()) { // Check if the file was successfully opened
    std::cout << "File content:" << std::endl; // Displaying a message indicating file content
    while (std::getline(file, line)) { // Read each line from the file
      std::cout << line << std::endl; // Display each line of the file
    }
    file.close(); // Close the file
  } else {
    std::cout << "Failed to open the file." << std::endl; // Display an error message if file opening failed
  }
}

// Function to calculate the average of numbers from a file
double calculateAverage(const std::string &filename) {
  std::ifstream file(filename); // Open file with given filename for reading
  double sum = 0.0; // Variable to store the sum of numbers
  double count = 0.0; // Variable to count the numbers

  if (file.is_open()) { // Check if the file was successfully opened
    double number; // Variable to store each number read from the file

    while (file >> number) { // Read each number from the file
      sum += number; // Add the number to the sum
      count++; // Increment the count of numbers
    }

    file.close(); // Close the file
  } else {
    std::cout << "Failed to open the file." << std::endl; // Display an error message if file opening failed
    return 0.0; // Return 0.0 if file opening failed
  }

  if (count > 0) { // Check if numbers were found in the file
    return sum / count; // Return the average of the numbers
  } else {
    std::cout << "No numbers found in the file." << std::endl; // Display a message if no numbers were found
    return 0.0; // Return 0.0 if no numbers were found
  }
}

int main() {
  std::string filename = "sample.txt"; // File containing numbers
  displayFileContent("sample.txt"); // Display content of "sample.txt"
  std::cout << std::endl; // Output a newline for formatting

  double average = calculateAverage(filename); // Calculate the average of numbers in the file
  std::cout << "Average: " << average << std::endl; // Display the calculated average
  return 0; // Return 0 to indicate successful execution
}

Sample Output:

File content:
100
200
300
500
600

Average: 340 

Explanation:

In the above exercise,

• The calculateAverage() function takes a filename and reads the numbers from the file using std::ifstream. It maintains a running sum of the numbers and a count of how many numbers are read.
• The program checks if the file has been successfully opened. If so, it reads each number from the file and updates the sum and count variables accordingly.
• After reading all the numbers, the file is closed.
• If the count is greater than 0, the average is calculated by dividing the sum by the count.
• If no numbers are found in the file, an appropriate message is displayed, and the average is set to 0.

Note: Content of a file is displayed using displayFileContent("filename.txt").

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C++ program to read numbers from a text file, calculate their sum and count, and then output the average.
• Write a C++ program that processes a file of integers, computes the average value, and displays the result with precision.
• Write a C++ program to open a file containing numeric values, sum them, and then calculate the average using file stream operations.
• Write a C++ program that reads a text file with numbers separated by spaces, computes the average, and handles invalid entries gracefully.

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