C++ introduction: what C++ is, where it's used, compilers, your first program, iostream, types, strings, control flow and functions

g++ -std=c++17 -Wall -Wextra hello.cpp -o hello
./hello

#include <iostream>
using namespace std;

int main() {
    cout << "Habari, Kenya!" << endl;
    cout << "Learning C++ on the Marzley learning hub." << endl;
    return 0;
}

#include <iostream>
using namespace std;

int main() {
    int students = 45;
    long long population = 53000000LL;
    double fee = 12500.75;
    char grade = 'A';
    bool paid = true;
    auto town = string("Kisumu");      // auto: the compiler infers the type
    const double VAT = 0.16;           // constant

    cout << "Students: " << students << ", population " << population << endl;
    cout << "Fee: " << fee << ", grade " << grade << ", paid " << boolalpha << paid << endl;
    cout << town << " VAT: " << VAT * 1000 << " on KSh 1000" << endl;
    cout << "int uses " << sizeof(int) << " bytes, double " << sizeof(double) << endl;
    return 0;
}

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

int main() {
    string first = "Wanjiku";
    string last = "Kamau";
    string full = first + " " + last;          // concatenation

    cout << full << " has " << full.length() << " characters" << endl;
    cout << "First letter: " << full[0] << endl;
    cout << "Surname starts at index " << full.find("Kamau") << endl;
    cout << "First 3 letters: " << full.substr(0, 3) << endl;

    string phone = "0712345678";
    if (phone.size() == 10 && phone[0] == '0') {
        string intl = "254" + phone.substr(1);
        cout << "M-Pesa format: " << intl << endl;
    }
    return 0;
}

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

int main() {
    string name;
    int age;
    cout << "Full name: ";
    getline(cin, name);          // reads a whole line including spaces
    cout << "Age: ";
    cin >> age;                  // reads one value
    cout << "Hello " << name << ", next year you'll be " << age + 1 << endl;
}

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

int main() {
    int mark = 72;
    if (mark >= 80) cout << "A" << endl;
    else if (mark >= 65) cout << "B" << endl;
    else if (mark >= 50) cout << "C" << endl;
    else cout << "Below C" << endl;

    int option = 2;
    switch (option) {
        case 1: cout << "Check balance" << endl; break;
        case 2: cout << "Send money" << endl; break;
        default: cout << "Invalid" << endl;
    }

    for (int i = 1; i <= 3; i++) {
        cout << "7 x " << i << " = " << 7 * i << endl;
    }

    vector<int> marks = {67, 82, 45, 90};
    int total = 0;
    for (int m : marks) {            // range-based for loop
        total += m;
    }
    cout << "Average: " << (double)total / marks.size() << endl;

    int months = 0;
    double balance = 0;
    while (balance < 50000) {
        balance = balance * 1.01 + 4500;
        months++;
    }
    cout << "Months to save 50,000: " << months << endl;
    return 0;
}

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

double vat(double amount, double rate = 0.16) {      // default argument
    return amount * rate;
}

void applyPayment(double &balance, double amount) {   // & = reference: changes the caller's variable
    balance -= amount;
}

string greet(const string &name) {                    // const reference: no copy, can't modify
    return "Hello, " + name;
}

int square(int x) { return x * x; }
double square(double x) { return x * x; }              // overloading: same name, different types

int main() {
    cout << vat(1000) << " " << vat(1000, 0.08) << endl;
    double fees = 25000;
    applyPayment(fees, 7500);
    cout << "Balance: " << fees << endl;
    cout << greet("Otieno") << endl;
    cout << square(5) << " " << square(2.5) << endl;
    return 0;
}

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

int main() {
    cout << fixed << setprecision(2);
    cout << setw(12) << "Item" << setw(10) << "Price" << endl;
    cout << setw(12) << "Laptop bag" << setw(10) << 2500.0 << endl;
    cout << setw(12) << "USB flash" << setw(10) << 900.0 << endl;
    return 0;
}