Question

Write up to 4 or 5 lines to explain the logic used behind those codes. Separately for each please

1) #include <iostream>

#include <string>

#include <fstream>

#include <vector>

#include <sstream>

using namespace std;

int main()

{

        ifstream infile("worldpop.txt");

        vector<pair<string, int>> population_directory;

        string line;

        while(getline(infile, line)){

                if(line.size()>0){

                        stringstream ss(line);

                        string country;

                        int population;

                        ss>>country;

                        ss>>population;

                        population_directory.push_back(make_pair(country, population));

                }

        }

        cout<<"Task 1"<<endl;

        cout<<"Names of countries with population>=1000,000,000"<<endl;

        for(int i=0;i<population_directory.size();i++){

                if(population_directory[i].second>=1000000000){

                        cout<<population_directory[i].first<<endl;

                }

        }

        cout<<"Names of countries with population<=1000,000"<<endl;

        for(int i=0;i<population_directory.size();i++){

                if(population_directory[i].second<=1000000){

                        cout<<population_directory[i].first<<endl;

                }

        }

}

2)

#include <iostream>

#include <string>

#include <fstream>

#include <vector>

#include <sstream>

using namespace std;

int main()

{

        ifstream infile("worldpop.txt");

        vector<pair<string, int>> population_directory;

        string line;

        while(getline(infile, line)){

                if(line.size()>0){

                        stringstream ss(line);

                        string country;

                        int population;

                        ss>>country;

                        ss>>population;

                        population_directory.push_back(make_pair(country, population));

                }

        }

        cout<<"Task 2"<<endl;

        cout<<"Names of first 10 countries"<<endl;

        for(int i=0;i<10;i++){

                cout<<population_directory[i].first<<endl;

        }       

}

3)

#include <iostream>

#include <string>

#include <fstream>

#include <vector>

#include <sstream>

using namespace std;

int main()

{

        ifstream infile("worldpop.txt");

        vector<pair<string, int>> population_directory;

        string line;

        while(getline(infile, line)){

                if(line.size()>0){

                        stringstream ss(line);

                        string country;

                        int population;

                        ss>>country;

                        ss>>population;

                        population_directory.push_back(make_pair(country, population));

                }

        }

        cout<<"Task 3"<<endl;

        cout<<"Names of last 10 countries"<<endl;

        for(int i=population_directory.size()-11;i<population_directory.size();i++){

                cout<<population_directory[i].first<<endl;

        }

}

Answer 1

Ok. I will help you. For each question, first, I will give a small explanation of what the whole program is doing, And along with that, I will add the same code you given with comments in it for better understanding.

Program 1 :

This program will open the file "worldpop.txt" which contains the country and population in each line.

A vector was created, where each item will be a pair of string and int. And this program will print two outputs

1. Names of countries with a population greater than or equal to 1000,000,000
2. Names of countries with population less than or equal to 1000,000

code:

#include <iostream>
#include <string>
#include <fstream>
#include <vector>
#include <sstream>
using namespace std;
int main()
{
    ifstream infile("worldpop.txt"); // open the file in the read mode
    vector<pair<string, int>> population_directory; // vector to store the contens of each line
    string line;
    while (getline(infile, line))   //read each line in the file
    {
        if (line.size() > 0)        // check if the line read was not empty
        {
            stringstream ss(line);  //Convert the line to the stringstream for easy type casting to other datatypes 
            string country;
            int population;
            ss >> country;          //converting the stringstream to string
            ss >> population;       //converting the stringstream to int type
            population_directory.push_back(make_pair(country, population)); // pushing the pair to the vector
        }
    } // after this loop, we will be having the vector with all the lines parsed and stored in it
    cout << "Task 1" << endl;
    cout << "Names of countries with population>=1000,000,000" << endl;
    for (int i = 0; i < population_directory.size(); i++)
    {
        //Retrieve each content in the vector
        // check if the population was above the required one 
        if (population_directory[i].second >= 1000000000)
        {
            cout << population_directory[i].first << endl; // Print the name of the country
        }
    }
    cout<< "Names of countries with population<=1000,000" << endl;
    for (int i = 0; i < population_directory.size(); i++)
    {
        //Retrieve each content in the vector
        // check if the population was below the required one 
        if (population_directory[i].second <= 1000000)
        {
            cout << population_directory[i].first << endl;// Print the name of the country
        }
    }
}

Program 2:

This program will open the file "worldpop.txt" which contains the country and population in each line.

A vector was created, where each item will be a pair of string and int.

And this program will print output which are the names of the first 10 countries in the file.

Code:

#include <iostream>
#include <string>
#include <fstream>
#include <vector>
#include <sstream>
using namespace std;
int main()
{
    ifstream infile("worldpop.txt");                // open the file in the read mode
    vector<pair<string, int>> population_directory; // vector to store the contens of each line
    string line;
    while (getline(infile, line)) //read each line in the file
    {
        if (line.size() > 0) // check if the line read was not empty
        {
            stringstream ss(line); //Convert the line to the stringstream for easy type casting to other datatypes
            string country;
            int population;
            ss >> country;                                                  //converting the stringstream to string
            ss >> population;                                               //converting the stringstream to int type
            population_directory.push_back(make_pair(country, population)); // pushing the pair to the vector
        }
    } // after this loop, we will be having the vector with all the lines parsed and stored in it
    cout << "Task 2" << endl;
    cout << "Names of first 10 countries" << endl;
    for (int i = 0; i < 10; i++)
    {
        // Iterate through the vector and prints the first 10 items (only the country name)
        cout << population_directory[i].first << endl;
    }
}

Program 3:

This program will open the file "worldpop.txt" which contains the country and population in each line.

A vector was created, where each item will be a pair of string and int.

Iterate through the vector and prints the last 10 items (only the country name)

for this to happen , we initialize the looping variable i to the size of the vector - 11 ,

becase then only we will get 10 elements. Then print those items

Code:

#include <iostream>
#include <string>
#include <fstream>
#include <vector>
#include <sstream>
using namespace std;
int main()
{
    ifstream infile("worldpop.txt");                // open the file in the read mode
    vector<pair<string, int>> population_directory; // vector to store the contens of each line
    string line;
    while (getline(infile, line)) //read each line in the file
    {
        if (line.size() > 0) // check if the line read was not empty
        {
            stringstream ss(line); //Convert the line to the stringstream for easy type casting to other datatypes
            string country;
            int population;
            ss >> country;                                                  //converting the stringstream to string
            ss >> population;                                               //converting the stringstream to int type
            population_directory.push_back(make_pair(country, population)); // pushing the pair to the vector
        }
    } // after this loop, we will be having the vector with all the lines parsed and stored in it
    cout << "Task 3" << endl;
    cout << "Names of last 10 countries" << endl;
    // Iterate through the vector and prints the last 10 items (only the country name)
    // for this to happen , we initialize the looping variable i to the size of the vector - 11 ,
    // becase then only we will get 10 elements. Then print those items
    for (int i = population_directory.size() - 11; i < population_directory.size(); i++)
    {
        
        cout << population_directory[i].first << endl;
    }
}