Vectors(cpp) Complete Guide ❤by Aryan

Claudio Ctin3 months ago6 mins

warning: use using namespace std:
i always use 1st based indexing

Introduction

#include <vector>
⛓ Vectors are arrays with super power (part of STL). You can sort it, push, pull data with just in-built(not recommended) functions.🧡🧡 It has one more superpower it size is very dynamic which means you can push any number of items even after size is specified.🧡 It just double the vector size.

initial size
(after adding) after size

0
1

2
4

note: Drawback of these vector is that memory wasteage. (getaway: always know no of items).

Syntax

Declaration

Usually you wont be needing vector without int(mainly).🧡

 // with specified size
 //(size,value) 
 //std::vector<datatype> arr_name(size);
 std::vector<int> file(5,12) // 5 elements with each 12
 std::vector<int> v(100); // Initializes 100 elements with zeros
 std::vector<int> v(existingVector) //create a copy of existingVector 

 // without size 
 // (initialize with zero size)
 // std::vector<string> name; 
 std::vector<string> str; //contains string value
 std::vector<bool> str2; //contains bool value
 std::vector<float> data = {1,2,3,4,5}; //vector with 5 value

built-in functions

import following header

#include <algorithm>

initial vector

std::vector<int> v = {1,5,4,3,2}

begin and end function

These are the pointer use to point the first and last element address

 auto first = v.begin();
 auto last = v.end();
 cout<<“first: “<<*first<< ” “<<“last: “<<*last<<ednl;

output

first: 1 last:2

SORT function

 //ascending order
 std::vector<int> v = {1,5,4,3,2};
 std::sort(v.begin(),v.end())

 //descending order
 std:sort(v.begin(),v.end(),std::greater<int>());
 // method 2
 //reverse iterator
 //use reverse iterator function
 //reverse iterator allows you to traverse vector in reverse order
 std::sort(v.rbegin(),v.rend())

output

 1 2 3 4 5
 5 4 3 2 1

Size function

know the no of elements in an array.

 v.size(); // 5

push_back function

append item at the end of the array

 std::vector<int> v = {1,5,4,3,2};
 v.push_back(5)

output

 1 5 4 3 2 5

pop_back function

remove the last item from vector

 v.pop_back(); //remove last item

output

1 5 4 3

back front function

returns the last element

 v.back() //3
 v.front() //1

insert function

insert item at given position

 std::vector<int> v = {1,2,3,4};
 //v.insert(position_pointer,size,value);
 // Insert 100 at position 4th (using an iterator)
 std::vector<int>::iterator it = myVector.begin() + 3;
 //(alternative)auto it = myVector.begin() + 3;
 myVector.insert(it,1,100);

output

1 2 3 100 4

erase function

This function helps erase element from specific position.

 v.erase(position) // remove ele from position
 v.erase(v.begin()) //remove the first element
 v.erase(v.begin() + 1) //remove 2nd element
 v.erase(v.end()) //revome last element

note:erase function always expect normal iterator

 //remove second last element
 auto itlast = v.rbegin();
 itlast++; // increase the iterator
 v.erase(itlast.base()) // remove second last element

note: convert the reverse iterator to normal one.

resize function

You can resize vector

clear function

You can clear function to remove all elements

empty function

 //check if it is empty or not
 if(v.empty())
 cout<<“yes”<<endl;

Ranged base loop

traverse vector using for loop

 for (int num : v) {
 cout << num << ” “;
 }

Accessing Values

put the index you want to access

 v[index]

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