CODEWITHSUNDEEP
c++vectorsize
zahra flower
zahra flower

Reputation: 51

How to define a vector with undefined size

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?

Upvotes: 5

Views: 8063

Answers (3)

Jeevan Prakash
Jeevan Prakash

Reputation: 776

Following code can be used to define vector of undefined size.

vector<string> v;

Remember that, for <string> you need following header file:

#include<string>

After all this you can push elements using push_back() function as follows-

v.push_back('a');
v.push_back('b');
v.push_back('c');
v.push_back('c');

There are some other useful functions for vectors you can give watch into-

front();
back();
begin();
end();
rbegin();
rend();    
max_size();
capacity();
resize();
empty();
at(n);

Read details of these function and their usage.

Upvotes: 1

Jaywalker
Jaywalker

Reputation: 3119

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.

Upvotes: 2

Joseph Mansfield
Joseph Mansfield

Reputation: 110658

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]);.

Upvotes: 5

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