CB100

 // El algoritmo utilizado para verificar que un numero es primo 
 // es la Criba de Eratóstenes 
 // https://es.wikipedia.org/wiki/Criba_de_Erat%C3%B3stenes
 
 #include <iostream>
 #include <fstream>
 #include <iomanip>
 #include <vector>
 #include <ctime>
 
 #define OUTPUT_FILE_PATH "primos.txt"
 const unsigned int MAXIMO = 100000000;
 
 void vectorDiscardNonPrimes(std::vector<bool> &v) {
     v[0] = v[1] = false; // 0 y 1 no son primos
     for (size_t i = 2; i*i < MAXIMO; ++i) {
         if(v[i]) {
             for (size_t j = i; j <= (MAXIMO/i); ++j) {
                 v[i*j] = false;
             }
         }
     }
 }
 
 void vectorPrintToOpenFile(
         const std::vector<bool> v,
         std::ofstream &outputFile,
         unsigned int &primesWritten) {
 
     primesWritten = 0;
     for (size_t i = 2; i < v.size(); ++i) {
         if(v[i]) {
             outputFile << i << std::endl;
             primesWritten++;
         }
     }
 }
 
 int main (void) {
     unsigned int startTime, primesFound;
     double totalTime;
     std::ofstream outputFile;
     std::vector<bool> numeros(MAXIMO, true);
     std::string timeUnit;
 
     startTime = clock();
     vectorDiscardNonPrimes(numeros);
 
     outputFile.open(OUTPUT_FILE_PATH);
     if (!outputFile.is_open()) {
         std::cerr << "ERROR: No se pudo abrir `" OUTPUT_FILE_PATH "`\n";
         return -1;
     }
 
     vectorPrintToOpenFile(numeros, outputFile, primesFound);
     outputFile.close();
     totalTime = (double(clock() - startTime)) / CLOCKS_PER_SEC;
 
     std::cout.precision(2);
     timeUnit.assign("segundos");
     if(totalTime < 1) {
         totalTime *= 1000;
         timeUnit.assign("ms");
         std::cout.precision(0);
     }
 
     std::cout << std::fixed
               << "Se encontraron `" << primesFound
               << "` números primos en `"
               << totalTime << "` " << timeUnit << std::endl;
 
     return 0;
 }