How to push an element into an array in C++? [duplicate] - c++

Question

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C++ array (Beginner)
(4 answers)
PUSH an array C++?
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Closed 6 years ago.
I need to write a function that:
Goes through all numbers from 50 to 100
Checks what numbers are divisible by 6
Adds those numbers to an array
Writes that array
Writes how many elements there are in that array
I've searched for a function push in c++ but looks like there is none...
Got this far, doesnt wok...
int pushIntoArray(int array[], int size){
int index = 0;
int newArray[100];
for (int i=0; i<=size; i++){
if(array[i] % 6 == 0 && array[i] <= 100 && array[i] >= 50){
newArray[index] = array[i];
index++;
}
}
}

Answer 1

You can't. Arrays ir C++ (and C too) are fixed-size. And for a good reason too. They are a very low level concept, quite similar to a pointer. The memory for an array is allocated once, at the start, and doesn't change after that. An array is just a bunch of bytes in memory.
A "push" operation would require to change the size of the array, which would mean allocating new memory, copying the contents from the old one, and deleting the old memory. And that's the simple, non-optimized version.
So, no, an array cannot do this. However the standard library includes a std::vector class which does exactly that and more. That's the one you want.

Answer 2

As said in the comment, when the size of an arrays isn't fixed, use std::vector
And use tham like in the code below:
#include <iostream>
#include <vector>
std::vector<int> pushIntoVector(std::vector<int> values) {
std::vector<int> result; //A vector of integers
for (int a : values) // Goes through each values of the vector
if (a <= 100 && a >= 50 && !(a % 6)) {
std::cout << a << "\n";
result.push_back(a);
}
std::cout << result.size() << "\n";
return result;
}
int main()
{
std::vector<int> vec;
vec.push_back(36); //Not printed: < 50
vec.push_back(60); //Printed
vec.push_back(72); //Printed
vec.push_back(90); //Printed
vec.push_back(91); //Not printed: 91%6 != 0
vec.push_back(105); //Not printed: > 100
pushIntoVector(vec); //Do whatever you want with the returned vector
while (1);
return 0;
}