New to C++, some pointers are needed.

ichigo@tea · 09-30-2008, 12:56 PM

Now, I'm not a complete newbie. I know what classes are, and I know what they do. I know the basics of OOP. but that's about it. I just have some questions I'd like to ask from people, and not a book.

First of all: I have a problem with my Geany IDE.

As you can see in this: http://img296.imageshack.us/img296/7109/geanygz8.png There's a backspace pwn. I'm using:

Code:

#include <iostream>

using namespace std;
int main()
{

	
	
	
	cout << "Enter your mpg: ";
	cin >> mpg;
}

I was wondering how to fix that one.

I played with C#, and I liked the idea of strings. I'm having trouble passing char arrays into a function. I was wondering how one may do this.

I know it looks something like:

Code:

char(char* greeting)

But I'm not sure.

I'll think of more to ask, my head is a bit cloudy atm with some personal issues.

virtualCoder · 09-30-2008, 01:16 PM

Quote:

Code:

#include <iostream>

using namespace std;
int main()
{

	
	
	
	cout << "Enter your mpg: ";
	cin >> mpg;
}

I dont know about your Geany IDE but you need to declare a variable to store anything read from standard input.

Code:

#include <iostream>

using namespace std;

int main()
{
  string mpg;  // For a reading a string.
//  int num;  // For storing numbers without decimals

  cout << "Enter your mpg: ";
  cin >> mpg;
  return 0;
}

nadroj · 09-30-2008, 01:23 PM

Quote:

As you can see in this: http://img296.imageshack.us/img296/7109/geanygz8.png There's a backspace pwn. I'm using:

Code:

#include <iostream>

using namespace std;
int main()
{

	
	
	
	cout << "Enter your mpg: ";
	cin >> mpg;
}

I was wondering how to fix that one.

what is a 'backspace pwn'? your code wont compile because 'mpg' isnt declared.

Quote:

I played with C#, and I liked the idea of strings. I'm having trouble passing char arrays into a function. I was wondering how one may do this.

I know it looks something like:

Code:

char(char* greeting)

But I'm not sure.

I'll think of more to ask, my head is a bit cloudy atm with some personal issues.

C++ was long before C#, and C++ came up with the string class first, so use that. to pass char arrays you can use what you have above. be careful not to go out of bounds with them when you are working with them in the function. if you are using a "char*", then use functions like "strlen" to get the length of the string so you know what the bounds are and dont go outside of them.

if you are passing a different kind of array, say int array, then there are two situations, for example:

Code:

void fooKnownArraySize(int ar[3])
{
  // here you are expecting an array with indices 0,1,2, so you know what the bounds are and it "should" work (ie the caller passed array of length 3
}

void fooNotKnowSize(int ar[])
{
  // this case would happen if you dont know the size of the array at runtime.  for example, reading a "string" from the user and converting each character
  // to its ASCII value and storing it into an int array (which is passed to this function). therefore the size of the array is determined at runtime
  // and this function doesnt know what size it is.
}

void fooNotKnowSize_fixed(int ar[], const int size)
{
  // this is similar to the previous function, however the size of the array IS known in the called function (ie where it looped over each character
  // to convert to ASCII, a count was kept). passing the int[] AND the known size of the array fixes this problem.
}

and finally, note that arrays are passed by reference, so changing them in a function will also change the array in the calling function. hope it helps

raconteur · 09-30-2008, 01:28 PM

I'm not quite sure what your first question is, so I'll leave that one for now, though I suspect what you mean is that entering a backspace at the prompt will produce undesired results -- if that is the case the answer is a bit more detailed than I feel up to this morning.

As for passing character arrays into a function, that is quite simple.
The address of the first element of an array and the address of a pointer to the array are identical.

The name of an array variable is synonymous with the address of first element of the array.

If your prototype is (i.e.):

Code:

int func(char *arg);

And your variable declaration is (again, i.e.):

Code:

char str[1024];

Then the call would be:

Code:

int ret = func(str);

This is all very basic C syntax, and you've said that you aren't exactly new to all this, so I'm a bit skeptical about whether I've really answered the question.

Arrays of character arrays are similar, and there are several methods for accessing them and passing them as arguments.