Making a function to shorten my code?

How can i make a function that does specific code like:

system("cls");
printf ("Testing...\n");
sleep(1);
system("cls");

Because in my program, i have hundreds of lines like these but i would rather define it in the beginiing as say "Test" and just write like the function "Test" everytime i want it do do these functions. How would i do this?

You're kidding, right? Any basic introductory text or online on C takes you through what is needed to create functions.

Have a look here for one of many online tutorials. That happens to be the first link I found by supplying "c function tutorial" to google.

Note that sleep() is not a standard C function and system("cls") is not guaranteed to always give the same results with different host systems. If you are already calling it, you're obviously don't care about that.

It looks like Test() is for debugging purposes. In this case one nice trick is to do something like this

Code:

---

void Test_noop_(void) {}
void Test_actual_(void) {printf("...Testing stuff goes here...\n");}

#ifdef NDEBUG
#define Test(...) Test_noop_()
#else
#define Test(...) Test_actual_()
#endif

---

Then, whenever you use Test() in your program, it will do your testing commands. Then later when you compile in release mode (e.g. with the -DNDEBUG switch), those debugging commands will be magically silenced without having to change your source code.

I wanted to use "test" as an example of a name for a function. But the commands would be the same if i named the function like "hello" or something?

Basically, naming functions is the same as naming variables. "hello" is as valid a name as "test" or "Test".
The only time the name matters is if the names you choose a name which clashes with other names elsewhere. E.g. suppose you name a variable or a function "printf" - then you're asking for trouble.

Also a better way to answer this question is to try it out yourself. Can you see any difference in your program if you name the function "hello" as opposed to "test"?

i get this error:
error: expected ';', ',' or ')' before '=' token
for this line:
void hello(const char *message, const char *testMsg="Testing...\n")

Code:

---

void hello(const char *message, const char *testMsg="Testing...\n")

---

Aren't default parameters illegal in 'C'? However, in 'C++' they are perfectly acceptable.

How could I re write it for c?

In C every function has a fixed number of parameters. Well, there are variadic functions but if you look at the header files these are actually macros which themselves call plain functions that, in the end, have a fixed number of arguments.

Anyway, if you really want to have "default arguments" a simple way is to specify a "wrapper function" that converts some default value, for example NULL in the case of a const char* into an appropriate default value of your choice. Example:

Code:

---

int main()
{
    hello("my message", NULL);  // use default argument for argument 2
    hello("my message", "my test msg");
    return 0;
}

---

So how do you write hello() in such a way that NULL is converted into "Testing...\n" ? Here is one way

Code:

---

void hello_ (const char *message, const char *testMsg) {
    printf("message is %s\n", message);
    printf("testMsg is %s\n", testMsg);
}

// void hello(const char *message, const char *testMsg = "Testing...\n");
void hello(const char *message, const char *testMsg)
{
    if (testMsg == NULL)    hello_(message, "Testing...\n");
    else                    hello_(message, testMsg);
}

---

If this case NULL is a magic value that you are using to mean to the function "I dont care about this parameter so just give me the default"