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Engineering LibreTexts

7.6: C++ Examples

  • Page ID
    10705
  • Strings

    #include <algorithm>
    #include <iostream>
    #include <string>
    
    using namespace std;
    
    string toLower(string);
    string toUpper(string);
    
    int main() {
        string str = "Hello";
    
        cout << "string: " << str << endl;
        cout << "tolower: " << toLower(str) << endl;
        cout << "toupper: " << toUpper(str) << endl;
        cout << "string.find('e'): " << str.find('e') << endl;
        cout << "string.length(): " << str.length() << endl;
        cout << "string.replace(0, 1, \"j\"): " << str.replace(0, 1, "j") << endl;
        cout << "string.substr(2, 2): " << str.substr(2, 2) << endl;
    
        string name = "Bob";
        double value = 123.456;
        cout << name << " earned $" << fixed << setprecision (2) << value << endl;
    
    }
    
    string toLower(string str) {
        transform(str.begin(), str.end(), str.begin(), ::tolower);
    
        return str;
    }
    
    string toUpper(string str) {
        transform(str.begin(), str.end(), str.begin(), ::toupper);
    
        return str;
    }
    

    Output

    string: Hello
    tolower: hello
    toupper: HELLO
    string.find('e'): 1
    string.length(): 5
    string.replace(0, 1, "j"): jello
    string.substr(2, 2): ll
    Bob earned $123.46
    

    Files

    // This program creates a file, adds data to the file, displays the file,
    // appends more data to the file, displays the file, and then deletes the file.
    // It will not run if the file already exists.
    //
    // References:
    //     https://www.mathsisfun.com/temperature-conversion.html
    //     https://en.wikibooks.org/wiki/C%2B%2B_Programming
    
    #include <fstream>
    #include <iomanip>
    #include <iostream>
    #include <string>
    
    using namespace std;
    
    double calculateFahrenheit(double celsius);
    void createFile(string);
    void readFile(string);
    void appendFile(string);
    void deleteFile(string);
    int fileExists(string);
    
    int main() {
        string FILENAME = "~file.txt";
    
        if(fileExists(FILENAME)) {
            cout << "File already exists." << endl;
        } else {
            createFile(FILENAME);
            readFile(FILENAME);
            appendFile(FILENAME);
            readFile(FILENAME);
            deleteFile(FILENAME);
        }
    }
    
    double calculateFahrenheit(double celsius) {
        double fahrenheit;
    
        fahrenheit = celsius * 9 / 5 + 32;
        return fahrenheit;
    }
    
    void createFile(string filename) {
        fstream file;
        float celsius;
        float fahrenheit;
        
        file.open(filename, fstream::out);
        if (file.is_open()) {
            file << "Celsius,Fahrenheit\n";
            for(celsius = 0; celsius <= 50; celsius++) {
                fahrenheit = calculateFahrenheit(celsius);
                file << fixed << setprecision (1) << celsius << "," << fahrenheit << endl;
            }
            file.close();
        } else {
            cout << "Error creating " << filename << endl;
        }
    }
    
    void readFile(string filename)
    {
        fstream file;
        string line;
    
        file.open(filename, fstream::in);
        if (file.is_open()) {
            while (getline(file, line))
            {
                cout << line << endl;
            }
            file.close();
            cout << endl;
        } else {
            cout << "Error reading " << filename << endl;
        }
    }
    
    void appendFile(string filename)
    {
        fstream file;
        float celsius;
        float fahrenheit;
        
        file.open(filename, fstream::out | fstream::app);
        if (file.is_open()) {
            for(celsius = 51; celsius <= 100; celsius++) {
                fahrenheit = calculateFahrenheit(celsius);
                file << fixed << setprecision (1) << celsius << "," << fahrenheit << endl;
            }
            file.close();
        } else {
            cout << "Error appending to " << filename << endl;
        }
    }
    
    void deleteFile(string filename)
    {
        remove(filename.c_str());
    }
    
    int fileExists(string filename)
    {
        FILE *file;
        
        file = fopen (filename.c_str(), "r");
        if (file != NULL)
        {
            fclose (file);
        }
        return (file != NULL);
    }
    

    Output

    Celsius,Fahrenheit
    0.0,32.0
    1.0,33.8
    2.0,35.6
    ...
    98.0,208.4
    99.0,210.2
    100.0,212.0