c++ vector

c++ vector

Vector is like array.
In array, you cannot change the length, but you can do that in vector.
It has index like array. syntax like "vector[3]= 3" is totally fine in vector

Format

std :: vector
     -> if you use "using namespace std", you do tno need to add "std ::"

constructor
     vector <type> name
     vector <type> name (length, val)
     vector <type> name (array , size of array)
         - type can be anything(string, int, char and other )

    .size()
        - return size of vector

    .insert( "interator", "val" )
        - add new element to vector. The element would be added at index. The elements in the vector shift one to right
        - you need iterator vector<int>::iterator 

    .push_back( "val" )
        - add new element to vector. The element will be stored at the end of vector. 

    .erase( "iterator" )
       - delete element of vector
       - if your vector is called input3, treat input3.begin() as index 0
                -> if you want to delete third element of vector, it would be input3.begin() +2
       - once the element is deleted, elements after deleted elements would shift one to left

    .clear()
       - delete all element of vector

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The following is practice code. If you have suggestion or correction, please feel free to leave comment.

#include <iostream>
#include <string>
#include <vector>

using namespace std;

int main(int argc, char** argv) {

    int array[] = {1,2,3,4};
   
    //1
    //constructors of vector
    vector <int> input (3,100); //length = 3 val = 100
    vector <int> input2 (array, array + sizeof(array) / sizeof(int));// constructor with array
    vector <int> input3;// empty vector
   
    //2
    //print element of vector. it is like array
    for(int i=0; i< input.size(); i++){
        cout << input[i] << endl;
    }
    cout << "----------------------------" << endl;
   
    //3
    //print element of vector. it is like array
    for(int i=0; i< input2.size(); i++){
        cout << input2[i] << endl;
       
    }
    cout << "----------------------------" << endl;
   
    //3
    //insert elements to vector
    //if you use insert, the vector element is stored at the very first index. the rest
    //are shift to right by one
    //if you use push_back, the vector element is stored at the end of vector
    vector<int>::iterator it;
    it = input3.insert(it , 300);
    it = input3.insert(it , 400);
    it = input3.insert(it , 100);
    input3.push_back( 999 );
   
    for (int i=0; i<input3.size(); i++){
        cout << input3[i] << endl;
    }
   
    cout << "----------------------------" << endl;
    //4
    //delete 2 elements of input3 vector
    //index(int) wont work. you need to use either begin or iterator
    input3.erase (input3.begin()+1);
   
    for (int i=0; i<input3.size(); i++){
    cout << input3[i] << endl;
    }
   
    cout << "-----------------------------" << endl;
    //5
    //clear all contents of vector
    input.clear();
    if (input.size() == 0)
        cout << "there is nothing in input vector" << endl;
    return 0;
}