How to define a vector with undefined size

Question

I am a beginner and I want to write a loop in cpp in which a vector has unknown size which is determined by a if funcion. basically I want to convert this MATLAB code to cpp code:

v(1)=A(1);
for i=2:length(A)
     if (abs((A(i)-v))>10^(-5))
       v=[v;A(i)];      
     end
end

It is clear in the code that the size of v is not determined before the loop starts, how can I write this code in cpp?

Answer 1

In C++, if we want a container of values that we can add values to and it expands at run-time, we use an std::vector. As you can see, it is aptly named for your purpose. The matlab line v=[v;A(i)];, which concatenates a value from A with v, is equivalent to using the std::vector::push_back function: v.push_back(A[i]);.

Answer 2

The standard C++ library has a class std::vector as indicated by one of the comments. The vector class doesn't have a pre-defined size; as you add member objects, the size of the vector grows dynamically. It might be worthwhile to read about standard C++ library in general and vector in particular.