test

prime_deng.cpp

/*
 // Skills included in this script:
 // (1) FOR loop;
 // (2) IF statement;
 // (3) Get the current time;
 // (4) Usage of vector (build, insert, size);
 // (5) How to convert int into string;
 // (6) Write into file;
 // (7) Output;
*/

//---------------------------------------------------------------------------------------------

// Preprocessor part
// They are special lines interpreted before the compilation of the program itself begins.
#include <iostream> // header
#include <fstream>  // use for file operation
#include <vector>

using namespace std;

int main() {
    
    // recorde the time the code starts
    time_t t1;
    t1 = time(NULL);
    
    
    int upper_limit = 100000;
    
    vector<int> result;
    
    for (int i = 0; i<=upper_limit; i++) {
        
        vector<int> temp_result;
        
        for (int j = 1; j<=i; j++) {
            
            if (i%j == 0) {
                temp_result.insert(temp_result.end(),j);
            }
        }
        
        if (temp_result.size()==2) {    // "1" and the prime number itself
            result.insert(result.end(), i);
        }
        
    }
    
    for (int k=0; k<result.size(); k++) {
        cout<<result[k]<<"\n";
    }
    
    cout << "There are "<<result.size() << " prime number from 0 to "<<upper_limit<<"\n";
    
    
    // write the results into a file
    // http://www.cplusplus.com/doc/tutorial/files/
    ofstream f;
    string temp_file_name = to_string(upper_limit);  // the easy way to convert an "int" into "string"
    f.open("/Users/nus/prime numbers from 1 to "+temp_file_name+".csv");
    for(int i=0; i<result.size() ;  i++){
        f << result[i] << "\n";
    }
    f.close();
    
    
    // recorde the time the code ends, and compute the time elapsed
    time_t t2;
    t2 = time(NULL);
    cout << t1 << endl;
    cout << t2 << endl;
    cout << t2-t1 << " seconds elapsed." << endl;
    
    return 0;
    
}