C++ Accelerated Questions Chapter 0.

As stated in an earlier topic I am trying to follow the exercises in this book. However the answers to the questions seem to be missing and can not be found online either (at least not to the majority of them). I am hoping some one can look my answers over for me.

Chapter 0.
0.0 Compile and run the "hello world" program.
Done.
0.1 What does the following statement do?

Code:

3+4;

It adds the number 4 to the number 3.
0.2 Write a program that, when run, writes: "This is a quote (") and this is a backslash (\).

Code:

#include<iostream> int main() { std::cout << "This (\") is a quote, and this (\\) is a backslash." << std::endl; return 0; }

0.3 The string literal "\t" represents a tab character; different C++implementations display tabs in different ways. Experiment with your implementation to learn how it treats tabs.
Done.
0.4 Write a program that, when run, writes the "hello, world!" program as its output.

Code:

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

0.5 Is this a valid program? Why or why not?

Code:

#include<iostream> int main() std::cout << "Hello, world!" << std:: endl;

No, the curly braces ({}) are missing in the main function.
0.6 Is this a valid program? Why or why not?

Code:

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

Yes, the program can be build. However the great amount of curly braces ({}) makes it hard to read.
0.7 What about this one?

Code:

#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; }

No, the comment stops between the words "and" and "as".
0.8 And this one?

Code:

#include<iostream> int main() { // This is a comment that extends over several lines // by using // at the beginning of each line instead of using /* // or */ to delimit comments. std::cout << "Does this work?" << std::endl; return 0; }

Yes this will work. The "//" will comment out everything places behind it on that line.
0.9 What is the shortest valid program?

Code:

#include<iostream> int main() { 3+4; }

0.10 Rewrite the "Hello, world!" program so that a new line occurs everywhere that white space is allowed in the program.

Code:

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

Well, except for 0.2, which is correct but the order of words, you only have one mistake here: your shortest program can be shorter. Try it. Why do you even have the include, you don't need it? And you don't even need that "3+4;" either, it does nothing at all... Try again and post it here.

Quote:

Originally Posted by EVOEx

Well, except for 0.2, which is correct but the order of words, you only have one mistake here: your shortest program can be shorter. Try it. Why do you even have the include, you don't need it? And you don't even need that "3+4;" either, it does nothing at all... Try again and post it here.

I thought the program had to do something in its function but hope this is better. Nothing is included and no calculations are made. It is made out of nothing more then the main functions skeleton.

Code:

int main() { }

Quote:

Originally Posted by Kitt3n

I thought the program had to do something in its function but hope this is better. Nothing is included and no calculations are made. It is made out of nothing more then the main functions skeleton.

Code:

int main() { }

Exactly. If you really want it the smallest you could also remove all whitespace. Try it; not that it matters but just so you can understand which whitespaces are mandatory and which can be left out.

Quote:

Originally Posted by EVOEx

Exactly. If you really want it the smallest you could also remove all whitespace. Try it; not that it matters but just so you can understand which whitespaces are mandatory and which can be left out.

I got it. For what I understood white space is meant for formatting the code to majke it more easy to read. So.

Code:

int main(){}

Could you also take a look at the next chapter that I posted. It would be nice for other people as well that try to use google to look for the answers to find a place where someone already overlooked all the answers.

Quote:

Originally Posted by Kitt3n

I got it. For what I understood white space is meant for formatting the code to majke it more easy to read. So.

Code:

int main(){}

Could you also take a look at the next chapter that I posted. It would be nice for other people as well that try to use google to look for the answers to find a place where someone already overlooked all the answers.

Perfect. That is, indeed, the very shortest legal program that can be written. Some would say "main(){}" would be valid; while according to some standards it is, it's not in C++.

I've already answered your chapter 1 questions.

Is the stuff in the code block for 0.4 the output of your program, or is it the program itself?

Quote:

Originally Posted by pianorain

Is the stuff in the code block for 0.4 the output of your program, or is it the program itself?

It is the program itself.

But the description asks you to write a program that writes the code for the Hello World program, not a program that writes Hello World.

Quote:

Originally Posted by CornedBee

But the description asks you to write a program that writes the code for the Hello World program, not a program that writes Hello World.

I got the question wrong then. I will rewrite it and post the corrected version in this topic later. I am currently trying to solve how to code a triangle using loops in the 3th chapter.

Quote:

0.1 What does the following statement do?

Code:

3+4;

I would argue that this code does nothing, as EVO said. So your answer is wrong. After all, if I tell you "3+4", what am I telling you to do? Nothing. It's as if I say "platypus."

Quote:

Originally Posted by CodeMonkey

I would argue that this code does nothing, as EVO said. So your answer is wrong. After all, if I tell you "3+4", what am I telling you to do? Nothing. It's as if I say "platypus."

I thought it added 3 to 4 but did not store the result in a variable but that it would still do the calculation.

Quote:

Originally Posted by Kitt3n

I thought it added 3 to 4 but did not store the result in a variable but that it would still do the calculation.

In the strict interpretation of the standard, it will. In reality, compilers will simply remove the calculation.

Quote:

Originally Posted by CornedBee

But the description asks you to write a program that writes the code for the Hello World program, not a program that writes Hello World.

Is this better?

Code:

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

Except for indentation, looks correct. But you shouldn't use endl every time you want a newline. Use \n within the string literals instead. endl flushes the stream, and you probably don't want that. In fact, I use endl very rarely, because you very rarely need to flush a stream explicitly. (Note that reading from cin flushes the stream implicitly.)

This could be a stupid question and already answered before but what exactly do you mean by flushing the stream?

Forced the data to to be seen at the screen (usually data is accumulated in a buffer and sent to the screen simultaneously because sending data to the screen is very slow).
I'd write it as:

Code:

#include<iostream> using std::cout; using std::endl; int main() { cout << "#include<iostream>\n" "\n" "int main()\n" "{\n" "\tstd::cout << \"Hello, world!\" << std::endl\n" "\n" "\treturn 0;\n" "}"; return 0; }

:D

Quote:

Originally Posted by Elysia

Forced the data to to be seen at the screen (usually data is accumulated in a buffer and sent to the screen simultaneously because sending data to the screen is very slow).
I'd write it as:

Code:

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

:D

Sorry for crashing the thread, but I often wondered why you would use endl over \n. So basically endl has greater overhead than \n?

Yes it would, since it would flush the output buffer.

Quote:

Originally Posted by Elysia

Yes it would, since it would flush the output buffer.

So if you just use \n. the output buffer would be flushed in a single go or when the buffer is full?

Not to be rude and interrupt the two of you but do you mean that using "endl" would make a separate call to the standard library therefor making it more slow then using \n?

Quote:

Originally Posted by Kitt3n

Not to be rude and interrupt the two of you but do you mean that using "endl" would make a separate call to the standard library therefor making it more slow then using \n?

I believe so, yes, since std::endl is actually a function. Hence it would flush everytime endl is called. While if you use "\n" if would probably only flush once (after you've printed the whole thing).
Can't say I know all the details, but this is the principle, at least.

Quote:

Originally Posted by Kitt3n

Not to be rude and interrupt the two of you but do you mean that using "endl" would make a separate call to the standard library therefor making it more slow then using \n?

Yes, though the forced flushing of the output buffer when encountering std::endl is more likely to be the main factor in slowing down the overall speed of output.

Thanks for the explanation.