Using arrays inside of function | Together C & C++ | Page 1

frigid timber Feb 16, 2023, 3:22 PM

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Im trying to like append the correct values inside of temperatures_cval but i dont get the result i would expect? dont know how to fix it tried also const int*


#include <stdio.h>


constexpr int no_value = -999;
constexpr int temperatures[]{ 10, 12, no_value, no_value, 20, 14, 6, -1, -5, 0, no_value, 1, -3 };

constexpr int size = sizeof(temperatures) / sizeof(int);
int temperatures_cval[size];


void without_no_value(const int array[], int size)
{
    int temp = temperatures[0];
    if (temperatures[0] == no_value)
    {
        temp = 0;
    }
    
    for (int i = 0; (i = size); i++)
    {
        if (temperatures[i] == no_value)
        {
            temperatures_cval[i] = temp;
            
        }else
        {
            temperatures_cval[i] = temperatures[i];
            temp = temperatures[i];
        }
    }
}

int main(){
    without_no_value(temperatures, size);
    for (int i = 0; (i = size); i++){
        printf("%i", temperatures_cval[i]);
    }
}

faint tideBOT Feb 16, 2023, 3:22 PM

#

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fallow atlas Feb 16, 2023, 3:25 PM

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What's up with that condition in for loop i=size

keen spruce Feb 16, 2023, 3:25 PM

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(i = size) is assignment, not comparison

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the loop will be infinite if size != 0

frigid timber Feb 16, 2023, 3:30 PM

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so it goes from 0 up to the size of the list array

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oh yes i changed it to <

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and it works

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great thanks

keen spruce Feb 16, 2023, 3:32 PM

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(◠‿◠✿)

frigid timber Feb 16, 2023, 3:35 PM

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i also deleted the const int array[] from the function

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becuase it wasnt needed is there something more i can do to make it more elegant

keen spruce Feb 16, 2023, 3:36 PM

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btw

constexpr int size = sizeof(temperatures) / sizeof(int);
int temperatures_cval[size];

can be written as

int temperatures_cval[std::size(temperatures)];

but you'd have to include <array>

#

if you need to access the size, may as well use std::array

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and

for (int i = 0; (i = size); i++)

can simply be

for (int temp : temperatures)

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C++ makes a lot of things easier

faint tideBOT Feb 16, 2023, 3:38 PM

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cppreference.com

std::size, std::ssize

template<class C>
constexpr auto size(const C& c)
    -> decltype(c.size());
// ... and 3 more

Defined in

#

cppreference.com

Range-based for loop (since C++11)

frigid timber Feb 16, 2023, 3:42 PM

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@keen spruce i dont really know if i can use all the things that cpp can provide.. as im learning C/CPP to program arduino for my uni course

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and i think it is done with C but sometimes using some stuff from cpp

keen spruce Feb 16, 2023, 3:43 PM

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well, even if you can't use the C++ standard library, you can at least use range-based for loops

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and writing your own std::size is trivial too, and might come in handy

frigid timber Feb 16, 2023, 3:44 PM

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keen spruce well, even if you can't use the C++ standard library, you can at least use range...

ranged based you mean by for (int temp : temperatures)

keen spruce Feb 16, 2023, 3:45 PM

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yes

frigid timber Feb 16, 2023, 3:49 PM

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@keen spruce is it better to have my find_min function like this or i should have a int minimum variable like i have temperaturs_cval

#include <stdio.h>

constexpr int no_value = -999;
constexpr int temperatures[]{ 10, 12, no_value, no_value, 20, 14, 6, -1, -5, 0, no_value, 1, -3 };

constexpr int size = sizeof(temperatures) / sizeof(int);
int temperatures_cval[size];


void without_no_value(int size)
{
    int temp = temperatures[0];
    if (temperatures[0] == no_value)
    {
        temp = 0;
    }
    
    for (int i = 0; (i != size); i++)
    {
        if (temperatures[i] == no_value)
        {
            temperatures_cval[i] = temp;
            
        }else
        {
            temperatures_cval[i] = temperatures[i];
            temp = temperatures[i];
        }
    }
}

int find_min(int array[])
{
    int minimum = array[0];
    
    for (int i = 0; i < size; i++)
    {
        if (array[i] < minimum)
        {
            minimum = array[i];
        }
    }
    return minimum;
}

int main()
{
    without_no_value(size);
    for (int temp : temperatures_cval)
    {
        printf("%i\n", temp);
    }
    
    printf("%i", find_min(temperatures_cval));
}

keen spruce Feb 16, 2023, 3:50 PM

#

it should be its own function, but it's very weird that the function isn't pure, but uses a global size

#

int find_min(const int array[], size_t size)
{
    if (size == 0) {
        // TODO: handle empty arrays
    }
    int minimum = array[0];
   
    for (size_t i = 1; i < size; i++)
    {
        if (array[i] < minimum)
        {
            minimum = array[i];
        }
    }
    return minimum;
}

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it could be written like this

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and then it's going to work for arrays of any size

frigid timber Feb 16, 2023, 3:52 PM

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why is there size_t size?

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when you are not using it in the function

keen spruce Feb 16, 2023, 3:54 PM

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wdym, it's used in size == 0 and i < size

frigid timber Feb 16, 2023, 3:57 PM

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yeah i didnt see that mb

faint tideBOT Feb 16, 2023, 4:02 PM

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@frigid timber Has your question been resolved? If so, run !solved :)

spark lily Feb 16, 2023, 4:06 PM

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keen spruce and ```cpp for (int i = 0; (i = size); i++) ``` can simply be ```cpp for (int te...

Doesn't range loops also work for c arrays?

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;compile

int a[] = {1, 2, 3};
for (int x : a)
    std::cout << x;

fathom cloakBOT Feb 16, 2023, 4:07 PM

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Program Output

fallow atlas Feb 16, 2023, 4:11 PM

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Why do they work though ;o

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If they decay to pointer it wouldn't work anymore ?

spark lily Feb 16, 2023, 4:11 PM

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Correct, but then it's not a c array, it is a pointer

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It works because there is an overload of std::begin for c arrays

fallow atlas Feb 16, 2023, 4:13 PM

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Ah interesting

keen spruce Feb 16, 2023, 4:13 PM

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fallow atlas If they decay to pointer it wouldn't work anymore ?

decay only happens to functions and arrays that are parameters of functions

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in that context, they're implicitly a pointer

fallow atlas Feb 16, 2023, 4:14 PM

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So when I'm making my own container , I can just use template specialisation for std begin and end ?

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Instead of making member functions

keen spruce Feb 16, 2023, 4:14 PM

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specializing anything in the standard library is undefined behaviour unless explicitly allowed

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if you want to be able to loop over your container, you just need to provide begin() and end() (member) functions

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but don't specialize std::begin

fallow atlas Feb 16, 2023, 4:18 PM

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Right I think my prof showed specialisation of std::hash for user defined class ,is that possible or I got STH wrong

keen spruce Feb 16, 2023, 4:19 PM

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yeah, that's because std::hash explicitly allows this

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it's meant to be used that way

fallow atlas Feb 16, 2023, 4:22 PM

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From cppreference
Each specialization of this template is either enabled ("untainted") or disabled ("poisoned")

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Does this mean it can be specialised ?

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I don't know where it says it's allowed

spark lily Feb 16, 2023, 4:30 PM

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Bonus points
std::ranges::begin will also look for begin function through argument dependent lookup.
So you can define a begin function wothout specializing std::begin

faint tideBOT Feb 17, 2023, 5:03 AM

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#Using arrays inside of function