C Frequently Asked Questions

Brace yourself, young noob. This C FAQ is a mighty distillation of ancient wisdom, gathered through the ages and across countless forum threads. It's the result of long, perilous quests, deep dives into messages long forgotten by time - and by search engines. Among its original authors are legendary figures such as Phoenix, Devlin and Darth JarJar - names whispered with awe in the coding underworld.

Yes, dear noob, every effort has been made to dazzle your eyes and enlighten your brain. So if one day, while wandering the SiteRaw forums, you spot someone asking a question that's already been answered here - don't hesitate to guide them towards this sacred scroll of knowledge.

This FAQ was built (mostly) from the most frequently asked questions on the C programming forums of www.siteraw.com, along with the battle-tested experience of its authors.

List of questions:

[1] User Inputs and scanf

[1][1] Why is scanf considered bad?
[1][2] Why shouldn't I use fflush on stdin?
[1][3] How do I clean up after scanf?
[1][4] How do I read integers with scanf/printf? What about floats?

[2] The Console

[2][1] How do I clear the console?

[3] Characters & Strings

[3][1] Why shouldn't I use char to store negative integers?
[3][2] How do I define a character?
[3][3] How can I get the ASCII value of a character?
[3][4] How do I define strings?

[4] Other C Questions

[4][1] Does the goto statement really exist in C?

User Inputs and scanf

99% of all programing problems come from the user. I don't know if this quote is actually true, but many developers certainly feel that way about user inputs in C. In this part, we will cover the infamous scanf and printff functions.

Why is scanf considered bad?

When scanf reads the input exactly as expected, everything mostly works out fine. But the moment a user types something unexpected, scanf basically gives up. It stops reading and leaves the input buffer in a messy state. If you try to use scanf again right after, it'll just keep tripping over the same leftover garbage and make things even worse.

In short: scanf doesn't clean up after itself — you have to do that part manually.

Here's a handy tutorial that shows how to live a happy, scanf-free life, and another one that teaches you how to use it properly (if you must).

Why shouldn't I use fflush on stdin?

Because the C standard says... nothing. It's undefined behavior. Which is a fancy way of saying: anything can happen. On some systems, it might work. On others, it might do absolutely nothing. Or worse — it might break things in ways that make your debugger cry.

So yeah, using fflush(stdin) is a bad idea. Just don't.

This rule applies to any input stream or file opened in read mode — or in read/write mode if the last operation was a read.

Nowadays fflush() is mostly used for output stream only, anyway.

How do I clean up after scanf?

To flush out whatever junk scanf left behind (especially when the user didn't follow the rules), you can loop through the input until you hit the newline character (\n):

void cleanscan(void)
{
    int c;
    do {
        c = getchar();
    } while (c != '\n' && c != EOF);
}

Or, you can use this little two-line trick:

// This line skips everything up to (but not including) the newline
scanf("%*[^\n]");
// And this one gobbles up the newline itself
getchar();

Either way, you'll be left with a clean input buffer and a clear conscience.

How do I read integers with scanf/printf? What about floats?

Each variable type has its own specific format string for scanf and printff. If you blindly use %ld and %lf for everything, expect bugs to show up at your doorstep.

It gets a little technical — don't go using entries with "C99+" on older compilers — but here's a quick breakdown:

For integers:

%hhd – signed char (C99+)
%hhu – unsigned char (C99+)
%d – int
%u – unsigned int
%ld – long int
%lu – unsigned long int

For floating-point values:

%f – float or double (for printff)
%f – float (for scanf)
%lf – double (for printff in C99+)
%lf – double (for scanf)

Use the right format, and your code will thank you. Or at least it won't explode.

The Console

How do I clear the console?

In purely standard (and portable) C, you can't. You need to use commands or functions from third-party libraries, which isn't recommended.

But what about system("cls"); and system("clear");?

This will just run the clearing command from Windows' Batch (with cls) or Unix' Shell (with clear). At best, you can use a #if defined(_WIN32) || defined(_WIN64) condition for those.

Characters & Strings

Why shouldn't I use char to store negative integers?

Because char is... ambiguous. Whether it can hold negative values depends on your compiler and system. It might work. Or it might not.

char will behave like either signed char or unsigned char, at the implementation's discretion. Most other types have a default of unsigned. If you need to store both positive and negative numbers, use signed char. It's explicitly made for that purpose.

How do I define a character?

You can define a character using either char or int. Here’s an example:

char char1 = 'a';
int char2 = 'a';
char char3 = 97;     // 97 is the ASCII value for 'a'
int char4 = 97;

printf("%c\n", char1);
printf("%c\n", char2);
printf("%c\n", char3);
printf("%c\n", char4);

Output:

a
a
a
a

No matter how you declare it — as a number or as a character — you'll get the same printed result if the value corresponds to a valid ASCII character.

How can I get the ASCII value of a character?

You've got two options:

Look it up in an ASCII table
Or just use this simple code

unsigned char c = '$'; // Let’s find the ASCII value of '$'
printf("%ld", (long int) c);

⚠️ Important: Use unsigned char. If you use char and the character comes from the extended ASCII set, you might end up with a negative value — which we told you is wrong.

The example above will print:

(Which is indeed the ASCII code for $.)

How do I define strings?

A string in C is just a character array, with one twist: it must end with a special \0 character that marks the end of the string.

// This string can hold 19 characters + the '\0' terminator
char s[20];

There are a few ways to initialize a string when you create it.

char str1[8];

// Initialize the second one right away
char str2[8] = "siteraw";

// Fill the first one manually
str1[0] = 's';
str1[1] = 'i';
str1[2] = 't';
str1[3] = 'e';
str1[4] = 'r';
str1[5] = 'a';
str1[6] = 'w';
str1[7] = '\0';

printf("%s\n", str1);
printf("%s\n", str2);

And the output:

siteraw
siteraw

Both versions do the same thing. Just make sure you don't forget the \0 at the end — it's what tells C where the string ends.