The University of Iowa
The College of Liberal Arts and Sciences
Department of Computer Science

Programming Languages and Tools:

CS:3210:0001

Lecture/Lab #2

Programming with C++

Namespaces, functions, std::string

Warm-up

main()
{
    return 0;
}

Is this a valid C++ program?

If so, what does it do?

Can it be simplified?

What happens if we try to return a string instead of an integer?

https://repl.it/@agurtovoy/lab2-warmup

Basics recap

Program execution starts with a function called main; we don't need to call main explicitly, the language runtime will do it for us when OS runs our program

The function body is enclosed in curly braces ({})

Individual statements within the function body are separated by semicolon (;)

Function declaration takes a general form of

<return-type> <function-name>( [<parameter list>] )

main's return type is int (short for integer), a standard built-in type representing integer numbers

int main()
{
    return 0;
}

Basics recap (cont.)

#include <iostream>

int main() {
    std::cout << "Hi there!\n";
}

To bring in symbol definitions from a standard (or a third-party) library, we need to #include a corresponding header

The standard header for console input/output is called iostream

To write something to the standard output, we use << operator on the standard output object, std::cout

main is special-cased to implicitly return 0, so we can omit the return statement

String literals are enclosed in double quotes (")

Similarly to Python, backslash character (\) inside of a string literal has a special meaning

Terminology

Python, etc.

C++

module / package

library, library header, header

import

include

import os

print( "Current directory:",
      os.getcwd() )

#include <iostream>
#include <filesystem>

int main() {
    std::cout 
       << "Current directory: " 
       << std::filesystem::current_path() 
       << "\n";
}

What about namespaces?

Because there is no explicit construct for declaring a namespace in Python or Java, the term might be unfamiliar to you...

... but the concept should not be.

A namespace is collection of names that exist independently of any other names in the program

In Python and Java this concept is tied to the notion of module/package: an entity declared in a module/package can be assigned any name you want, because when you import the module/package, its entities will be scoped within the module/package's namespace:

import os
print( os.getcwd() )

Namespaces in C++

In C++, namespaces exist independently of the physical structure of the program

Specifically, there is no one-to-one correspondence between a namespace and a library header (C++ equivalent of a module/package):

#include <iostream>
#include <filesystem>

int main() {
    std::cout 
       << std::filesystem::current_path() 
       << "\n";
}

Instead, C++ gives us construct to explicitly define and manage namespaces independently of what file we put our code into

Exercise 1

Write a program that prints the following two lines of text to the standard output:

https://repl.it/@agurtovoy/lab2-exercise1

Open the exercise template

Write your code, press Run to test

When you're done, grab your Repl's link and send it as a direct message to me (agurtovoy)

Click on the corresponding option in the "Lab2 exercises" poll in #general

Hello, Bob!
Nice to meet you

Instructions

Functions

https://repl.it/@agurtovoy/lab2-functions

#include <iostream>

int main()
{
    hello_world(); // print "Hello from a function!"
    return 0;
}

void return type is used to designate that a function doesn't return a value

Function call syntax in C++ is the same as in many other mainstream programming languages:

<function-name>( [<comma-separated argument list>] )

A function (and, more generally, any other program entity) needs to be declared before we can use it in the program

Exercise 2

Refactor your Exercise 1 solution by moving the console output code inside of the following two functions:

https://repl.it/@agurtovoy/lab2-exercise2

Open the exercise template

Write your code, press Run to test

When you're done, grab your Repl's link and send it as a direct message to me (agurtovoy)

Click on the corresponding option in the "Lab2 exercises" poll in #general

Instructions

int main() {
    hello_bob();
    nice_to_meet_you();
}

Passing function arguments

int main()
{
    hello("Bob"); // print "Hello, Bob!"
}

https://repl.it/@agurtovoy/lab2-function-calls

A function can be declared to have one or more parameters

We have to specify a type for each of the parameters

Mismatch in type/number of function arguments is detected at compile time

String literals are best passed as std::strings

Parameters at the end of function parameter list can be supplied default arguments