Thread: Some basic things

Originally Posted by dwks

Code:

for (int i = 0; i < strlen(my_str); i++)

Consider calculating strlen() outside of that loop -- it's rather expensive in time to compute for every iteration of the loop.

But then again, most of the times, it shouldn't have noticable performance impact at all unless your code is really time critical.

Originally Posted by dwks

Code:

std::string my_str; // We're assuming the text is stored in my_str

We're assuming we're in the C++ forum unfoundedly, eh?

LOL, yes! But it doesn't matter if it's std::string or char* or whatever. The princip if the same.

Originally Posted by Nathalie

Okay, thanks for explaining once again! One tiny question more: how do you print the result of the a^b thing?

To the console screen?
In C++, I'd use cout, but since this C... meh.

Code:

fprintf(stdout, "%i", num)

?

Nope. fprintf() takes for its first parameter a FILE* stream, which you can specify as stdout; but printf() automatically prints to stdout. [edit] No fair editing. [/edit]

I'm sure you can figure it out. Just modify your own code! (I replaced the quotes.)

Code:

printf("min %d", min);

And you'd want a newline on the end, most likely.

[edit]

But then again, most of the times, it shouldn't have noticable performance impact at all unless your code is really time critical.

There probably wouldn't be much of a difference, it's true, but is it really that much harder to declare a variable, save the result in that, and use that variable in the loop expression? strlen() has to iterate over every character in the string, comparing them to 0. It's likely more time-consuming than the rest of your loop put together. [/edit]

Originally Posted by Nathalie

Hard to follow a bit, but thanks anyway. Although I have another small problem, which is that for some reason whatever C Compiler I use, it refuses to build or compile anything. I downloaded and tried Dev-C++ as you recommended, and although it seems easy to use, this too says: " C:\Dev-Cpp\Makefile.win [Build Error] [main.o] Error 1 " when I hit F9.

I did this with a standard Hello World code I found online, which shouldn't contain any errors. This explanation may be a bit vague, but any idea what is going on?

What is your path? Dev-C++ requires the path to be modified before it can compile anything. On Windows Vista this can be a real pain, and you have to do it yourself.

What operating system are you using? Did you try modifying the path yourself already?

ETA: dwks, that means I have to replace every “%d” by some other text? What kind of? I didn't write that code, I asked somebody else for help but he was unable to explain or go on any further.

Here's a brief summary of how printf() works.

Any characters except '%' printf() prints verbatim to stdout (which is usually the screen, but can be redirected to a file if the user wishes). When printf() sees a '%', it checks the next character. If it's an 's', printf() is expecting a string; a 'd' or an 'i', it looks for an int. It then takes the next parameter that was passed to it, treating it as an int or a string or whatever, and prints that.

For example:

Code:

const char *name = "John";
int age = 42;
printf("Hello, %s! I hear you are %d years old.\n", name, age);

Oh yeah, I forgot about backslashes. When the compiler sees a backslash in a string, it treats the next character specially. "\n" is a newline (like what happens when you press <enter>), "\t" is a tab, and "\\" is a backslash itself.

printf()'s format specifiers are easy to find online: http://www.cplusplus.com/reference/c...io/printf.html
And escape sequences like "\n" are too: http://www.cppreference.com/escape_sequences.html

Originally Posted by Nathalie

Oh, I didn't know about the paths, that must be the reason. Personally I use Windows Vista, but my friend has Windows XP. Perhaps it is easier to make it work on that? In the end I just wanted to figure it out for him, but I don't need it (although I am interested in programming and wouldn't mind trying).

If you could explain how to configure the path (XP method is fine), I will have him try it when he gets home.

For XP, see the bottom of this page. http://www.computerhope.com/issues/ch000549.htm

You'll want to add C:\Dev-C++\Bin to the end of the path. Or where ever you installed Dev-C++.

I can't find anything about Vista, and I can't remember how I did it. But next time I'm on my Vista computer I can figure it out for you if you like.

I think it was Start->Right click on Computer->Properties->Advanced->Environment Variables or something. Who knows.

Since Dev-C++ appears to be installed in C:\Dev-Cpp, add

Code:

;C:\Dev-Cpp\Bin

to the end of your PATH variable. In the bottom scrollbox, scroll until you see PATH, then click edit (or whatever the Dutch for that is!), and type that at the end.

Does anyone know why it isn't working?

I believe you have a couple of compile errors: you are missing the terminating semi-colon on line 3, and your for loop is not correct (hint: commas versus semi-colons).

Aside from these errors, you might want to move your variables to main() such that they are no longer global variables. It makes no difference in this case, but it is good practice.