Foundations

Hello C++

Start with a tiny C++ program that stores a name and prints a greeting.

cout `std::cout` writes text so you can see what the program produced.

Hello C++

name
hello.cpp
Replay: real traced execution (multi-file project)
#include <iostream>
#include <string>

int main() {
    std::string name = "C++";
    std::string message = "Hello, " + name + "!";

    std::cout << message << std::endl;
    return 0;
}

#include <iostream>
#include <string>

int main() {
    std::string name = "Ada";
    std::string message = "Hello, " + name + "!";

    std::cout << message << std::endl;
    return 0;
}

#include <iostream>
#include <string>

int main() {
    std::string name = "Bjarne";
    std::string message = "Hello, " + name + "!";

    std::cout << message << std::endl;
    return 0;
}

  1. name ← C++, message ← Hello, C++!

    4int main() {5    std::string name→ C++ = "C++"; //@name="Ada", "Bjarne"6    std::string message→ Hello, C++! = "Hello, " + nameC++ + "!";78    std::cout << messageHello, C++! << std::endl;9    return 0;10}
    outputHello, C++!

  1. name ← Ada, message ← Hello, Ada!

    4int main() {5    std::string name→ Ada = "Ada";6    std::string message→ Hello, Ada! = "Hello, " + nameAda + "!";78    std::cout << messageHello, Ada! << std::endl;9    return 0;10}
    outputHello, Ada!

  1. name ← Bjarne, message ← Hello, Bjarne!

    4int main() {5    std::string name→ Bjarne = "Bjarne";6    std::string message→ Hello, Bjarne! = "Hello, " + nameBjarne + "!";78    std::cout << messageHello, Bjarne! << std::endl;9    return 0;10}
    outputHello, Bjarne!

Follow the Greeting

  1. name starts as "C++".
  2. The program joins "Hello, ", name, and "!".
  3. message becomes Hello, C++!.
  4. std::cout prints Hello, C++!. | name | message | | --- | --- | | C++ | Hello, C++! | | Ada | Hello, Ada! | | Bjarne | Hello, Bjarne! |

Exercise: hello.cpp

Reproduce Hello, C++!, then try Ada and Bjarne and predict each greeting before running it.