Could someone please walk through this code step-by-step?

[DELB]

float pos[3] = {0.0f, 0.0f, 0.0f};

float distance(float mob1[3], float mob2[3])
{
    return sqrt(sqr(mob2[0]-mob1[0]) + 
                sqr(mob2[1]-mob1[1]) + 
                sqr(mob2[2]-mob1[2]));
}

It comes from this tutorial: http://noobtuts.com/programming/c-plus-plus/tutorial-for-noobs-part-8-arrays.

Thanks. Is there also a way to make this print something out on the screen so that I can see what is happening? I find it easier to learn when I can see an output.

[j3Rz8vqX]

The link you provided is no longer available or has an issue with its address, it displays: "The page has not been found".

The address that worked for me is:
noobtuts.com/programming/c-plus-plus/tutorial-for-noobs-part-8-arrays

BTW: The sqrt function was called incorrectly in the post, so I've fixed it.
It should be sqrt, not sqr.

float pos[3] = {0.0f, 0.0f, 0.0f};
/*
   Declares an array of float,
      with a size of 3,
      with three values of 0 with the data type of float.
*/

float distance(float mob1[3], float mob2[3])
{
/*
   A function or method that takes two arrays of type float
      with each array having a size of 3
*/
    return sqrt(sqrt(mob2[0]-mob1[0]) + 
                sqrt(mob2[1]-mob1[1]) + 
                sqrt(mob2[2]-mob1[2]));
/*
   the square root of mob2[2] - mob1[2] plus
   the square root of mob2[1] - mob1[1] plus
   the square root of mob2[0] - mob1[0] then

   taking the square root of the resulting sum and

   returning a float
*/    
}

In the above code, and at it's corresponding site: In the array tutorial, they never call the distance formula once.

You can find the resulting float by simply calling this function with cout.

Note, that it would have 2 arrays of type float, with at least 3 data.

An example would be like this:

#include <iostream>
#include <cmath>
using namespace std;

float distance(float mob1[3], float mob2[3])
{
    return sqrt(sqrt(mob2[0]-mob1[0]) + 
                sqrt(mob2[1]-mob1[1]) + 
                sqrt(mob2[2]-mob1[2]));
}

int main()
{
   float float_arr1[3] = {6.0f, 2.0f, 12.0f};
   float float_arr2[3] = {22.0f, 27.0f, 48.0f};

   cout<<"result: "<<distance(float_arr1,float_arr2)<<endl;
   cout<<"Press enter or return to exit: "<<endl;
   cin.get();
   return 0;
}

[DELB]

Thanks man. Sorry about the link. Also, it mentions that this code finds the distance, what would the units be? Metres^2 I presume?

I'm on this part now:
http://noobtuts.com/programming/c-plus-plus/tutorial-for-noobs-part-10-strings

If you scroll down to the bottom it has the following code:

std::string a = "abc";
std::string b = "bcd";
if (a == b) {
    std::cout<<"equal!";
}

std::string a = "abc";
std::string b = "bcd";
if (a.compare(b) == 0) {
    std::cout<<"equal!";
}

I don't really get what it means. If I use this code I get the same result despite the tutorial saying that it's different. Perhaps someone could go into this more in-depth?

[j3Rz8vqX]

You can actually validate if a string is equal by just applying the equality operator.

In the tutorial that you were reading, the editor was stating that the two compares were a bit different.


== can only return a boolean


std::string compare can returns a negative, 0, or positive value depending on the difference of the two strings.
http://www.cplusplus.com/reference/string/string/compare/
(Check the possible return values - located in the box diagram)

Here's what others have got the say about it:
http://stackoverflow.com/questions/9158894/differences-between-c-string-and-compare

Both compares strings.

One uses the standard comparison method (==)
and the other uses string's comparison method.

[DELB]

I see, I see.

What does the == !0 do? I've tested it out and I'm thinking that it means "if string is not the same then do..." in my head. I don't get a result if my code is this:

#include "stdafx.h"
#include <iostream>
#include <cmath>
using namespace std;

int main()
{
	std::string a = "abc";
	std::string b = "fda";
	if (a.compare(b) == !0) {
		std::cout << "not equal";
	}
	cin.get();
	return 0;
}

[j3Rz8vqX]

The not(!) typically means its opposite.

Since booleans have only two possibilities (true and false), !0 would be 1.

http://www.cplusplus.com/doc/boolean/

1 usually represents yes/true, 0 usually represents no/false.

If (a.compare(b) == !0) //If (compare's returned value) (is equal) (not false); Not false literally means true(1).

Using the reference from before:
http://www.cplusplus.com/reference/string/string/compare/

a.compare(b) will return a value less than 0 (<0) because its first character 'a', from string a, has a smaller integer value than 'f', from string b; in this case, you got -1.

Normally it would return 0 if a complete match was found, and a value greater than 0 if the first string was larger; aka 1.

http://www.asciitable.com/
'a' = 97
'f' = 102

So, if (-1) (is equal to) (not false(0) aka true(1))
print out "not equal"

This would never happen, since boolean could only have a value of 0 or 1

This could be consider an undefined behavior, because we were expecting any value that was not 0 to be valid, but in this case, -1 was also not valid.

If your carious as to what the result of the comparison was you can try this code:

#include "stdafx.h"
#include <iostream>
#include <cmath>
using namespace std;

int main()
{
	std::string a = "abc";
	std::string b = "fda";
	cout<<"Result of comparison of string a and string b: "<<a.compare(b)<<endl;
	cout<<"Result of comparison of string b and string a: "<<a.compare(b)<<endl;
	if (a.compare(b) == !0) {
		std::cout << "not equal";
	}
	cin.get();
	return 0;
}

Edit: Posted at 3 AM, hopefully it's legible.

[DELB]

I'm not home at the moment so lemme run through this and tell me if it's right.

So basically, !0 is true? So 0 is false? That's correct?

So, since "a" has a lower value on the ASCII chart (it's 97) then I would get <0, this isn't possible because boolean has only 0 and 1 which means true or false and I would get no output.

However, if I say put "g" in-place of "a" I would get >0 which is 1? But if both were the same, I'd get a 0?

[TwilightSpectre]

Sorry for jumping back to an earlier part of the thread, but the distance from one point to another (in three dimensional space) is defined as:

mod(v2 - v1)

Which in turn equals:

sqrt((v2.x)2 - (v1.x)2 +
     (v2.y)2 - (v1.y)2 +
     (v2.z)2 - (v1.z)2)

Which is a scalar value, hence the result being in units.

Also, false is defined as being the value zero, and true is anything that isn't false. Hope that clears things up.

[DELB]

I see. Thanks. However, is it possible to get a 1 when there is an output? I only seem to get -1 when the values are same and 0 when it's not the same. Ah, was said above. I'll have to potch about more when I get home.

[j3Rz8vqX]

#include "stdafx.h"
#include <iostream>
#include <cmath>
using namespace std;

int main()
{
	std::string a = "abc";
	std::string b = "fda";
	cout<<"Result of comparison of string a and string b: "<<a.compare(b)<<endl;
	cout<<"Result of comparison of string b and string a: "<<b.compare(a)<<endl;//Was Edited to implement the correct opposite test
	if (a.compare(b) == !0) {
		std::cout << "not equal";
	}
	cin.get();
	return 0;
}

My apologies, at 2 AM i'm not my best.
The above code now shows that it is 1, when comparing b to a.