Exercise 0-9

What is the shortest valid program?

Solution

According to chapter 0 (Getting Started) of the book Accelerated C++ …

On Main function:

• Every C++ program must define exactly one function, named main, that returns an int.
• The implementation runs the program by calling main.
• A zero returns indicates success; a non-zero return indicates failure.
• In general, functions must include at least one return statement and are not permitted to fall off the end of the function.
• The main function is special: it may omit the return; if it does so, the implementation will assume a zero return value.
• However, explicitly including a return from main is good practice.

The shortest valid program can therefore be as short as a one-liner like this (or can this be made even shorter I wonder?)

int main() {}

Result

The program compiles okay in Code::Block and gives me the following output the the console output window.

Process returned 0 (0x0)   execution time : 0.141 s
Press any key to continue.

Reference

Exercise 0-7

Is this a valid program? why or why not?

#include <iostream>
int main{}
{
    /* This is a comment that extends over several lines
       because it uses /* and */ as its starting and ending delimiters */
       std::cout << "Does this work?" << std::endl;
       return 0;
}

Solution

No. This is not a valid C++ Program.

The issue is the way the code treats comment. A correct block-comment looks like this.

/* this is a comment */

i.e. a correctly written comment is surround by the /* and */. Anything in between is a comment. Anything outside is not a comment.

In this case, the actual comment part is highlighted in blue below (and the remaining red part is not qualified as a comment)

/* This is a comment that extends over several lines
because it uses /* and */ as its starting and ending delimiters */

I would correct the comment to something like this (using the line comment //), should we wish to keep the comments.

// This is a comment that extends over several lines
// because it uses /* and */ as its starting and ending delimiters

Reference

Exercise 0-6

Is this a valid program? Why or why not?

#include <iostream>
int main() {{{{{{std::cout << "Hello World!" << std::endl;}}}}}}

Solution

Yes. This is a valid C++ program.

In C++ curly braces tell the implementation to treat whatever (statement) appears between them as a unit.

It is okay to have nested curly braces, as long as all the curly braces are balanced out. i.e. for every single open/left brace it is matched by a close/right brace.

Let’s run the program and see what we get?

Result

The program compiles okay. And gives us the following result in the console output window.

Hello World!

Process returned 0 (0x0)   execution time : 0.187 s
Press any key to continue.

Experiment – Nested Curly Braces

Let us, for curiosity sake to see if nested curly braces actually work? Here is a very simple program that I write for this experiment.

// Experiment with nested curly braces
#include <iostream>
int main()
{
    std::cout << "I am block 1" << std::endl;
    {
        std::cout << "I am block 1-1, son of block 1" << std::endl;
        {
            std::cout << "I am block 1-1-1, son of block 1-1, grandson of block 1." << std::endl;
            std::cout << "I am block 1-1-2, son of block 1-1, grandson of block 1." << std::endl;
        }
    }
    {
        std::cout << "I am block 1-2, son of block 1" << std::endl;
    }
}

The program compiles okay and gives us the followings in the console output window as expected.

I am block 1
I am block 1-1, son of block 1
I am block 1-1-1, son of block 1-1, grandson of block 1.
I am block 1-1-2, son of block 1-1, grandson of block 1.
I am block 1-2, son of block 1

Process returned 0 (0x0)   execution time : 0.187 s
Press any key to continue.

This experiment has demonstrated that nested curly braces essentially provides a way to group blocks of statements together, which I think is a very cool feature as it allows us breakdown tons of statements into smaller blocks. This is very handy if we are to define a chunky function.

Reference

Exercise 0-4

Write a program that, when run, writes the Hello World program as its output.

Solution

Using the skills picked up from the previous exercises, this should be quite a straight forward exercise. There is nothing new here. Below is my code (of course, there are many ways to do this.)

#include <iostream>
int main()
{
    std::cout << "#include <iostream>" << std::endl;
    std::cout << "int main()" << std::endl;
    std::cout << "{" << std::endl;
    std::cout << "  std::cout << \"Hello World!\" << std::endl;" << std::endl;
    std::cout << "  return 0;" << std::endl;
    std::cout << "}" << std::endl;
    return 0;
}

Result

Submitting the program produces the Hello World code in the console output window.

#include <iostream>
int main()
{
  std::cout << "Hello World!" << std::endl;
  return 0;
}

Process returned 0 (0x0)   execution time : 0.179 s
Press any key to continue.

# Reference

Koenig, Andrew & Moo, Barbara E., Accelerated C++, Addison-Wesley, 2000