Hi i've started learning to program C++ some weeks ago. I have this pdf book that i learn from but i have run into some troubble with a program. The program is as stated here:

#include
using namespace std;

void cube(int *n, num);

int main()
{
int i, nums[10];

for(i = 0; i < 10; i++) nums = i + 1;

cout << "Original contents: ";
for(i = 0; i < 10; i++) cout << nums << ' ';
cout << '\n';

cube(nums, 10);

cout << "Altered contents: ";
for(i = 0; i < 10; i++) cout << nums << ' ';

return 0;
}

My book tells me to write that. It should show something about array passing from one function to another but i simply cant get it to do as its supposed to. I use borland c++ compiler 5.5 to compile with.

please help me.
Sincerly
Vikkenhi..vikken.!
i'm just wondering if that code is correct or n0t..
the 'nums[10]' variable was DECLARED as an array right? now, in your code inside the for loop, you assign a value to the variable 'nums' which is n0t an array, coz' it does n0t have []..why n0t try to make it nums[ i ]=i+1;

..hope it helps.!actually, it does include the indexing square brackets, but since it was directly in the post, the forum interpreted the [ i ] (without spaces) as an italics TAG.

here is the full code, in a helpful code tag

Code: [Select]#include <iostream>
using namespace std;

void cube(int *n, num);

int main()
{
int i, nums[10];

for(i = 0; i < 10; i++) nums[i] = i + 1;

cout << "Original contents: ";
for(i = 0; i < 10; i++) cout << nums[i] << ' ';
cout << '\n';

cube(nums, 10);

cout << "Altered contents: ";
for(i = 0; i < 10; i++) cout << nums[i] << ' ';

return 0;
}


Since I'm here, I may as well offer some relevant help;

The first thing that jumps out is that although you declare the "cube" function, you haven't provided a DEFINITION for it; therefore my attempts to compile as-is give me unresolved externals.

However, I added this definition in, so I could proceed to test:

Code: [Select]void cube(int *n, int num)
{

for(int i=0;i<=10;i++)
n[i]=n[i]*num;


}

Pretty simple; it simply multiplies each element of the 11 element array (as you declared it; note that declaring a variable like variable[n] will create a array with n as the highest index; therefore you get n+1 elements, since 0 is the lower bound.)

I get the following output, which confirms that it works:


Code: [Select]Original contents: 1 2 3 4 5 6 7 8 9 10 11
Altered contents: 10 20 30 40 50 60 70 80 90 100 110
(I also changed the for loops from " for(i = 0; i < 10; i++)" to " for(i = 0; i <= 10; i++)")


It definitely seems that it works just fine.

truthfully, the square brackets are actually memory indexing operators; you can use them on any type in C, but C++ restricts their use and you get warnings when you do freaky stuff sometimes, but largely, it's possible to use it for nearly anything. Any pointer type, for example, can be indexed into.

with a pointer type (in the "cube" prototype, the first parameter is being passed as a pointer to a int) when you use the array/memory indexing operator (the square brackets) it returns the value in memory at the pointers position plus the array index times the array size. For example, lets say you have a char array "chars" and it contains the string "characters". with a pointer, you can do something like this:
Code: [Select]char *charsp = &chars[0];
singchar = charsp[4];
It looks pretty straightforward, but remember, charsp is not an array type! so how does it work? As I said, it's indexing directly into memory at that location based on the passed index. with your standard char, this means it is accessing the 4th byte after the byte pointed to by the char itself (in this case the first one). However, if instead of char types we were dealing with, say, wide characters, then each char would be two bytes, so the indexing would do the math of 4*2, so it would grab the two byte character at position 10 (we add two because the first element is also two bytes).

I hope this helps clear things up; you weren't specific as tou what kind of trouble you were running into, and the code you provided works fine for me (Visual Studio 2008, btw) So I thought I'd see if I could help clarify the array/pointer business.BCP, I see you cleverly understood what a "cube" function should return... it's always good to help people get top marks for their homework.


Quote from: Salmon Trout on November 14, 2010, 10:24:19 AM

BCP, I see you cleverly understood what a "cube" function should return... it's always good to help people get top marks for their homework.

Thank you very much it was very helpful

actually, it does include the indexing square brackets, but since it was directly in the post, the forum interpreted the [ i ] (without spaces) as an italics tag.