C++开发EOS基础指南

// @url: https://repl.it/@MrToph/CPPBasics-1
// In c++ libraries are imported through the #include macro
// iostream comes with functions handling input and output to the console
#include <iostream>
// includes rand function
#include <cstdlib>
// includes time function
#include <ctime>

// this is how to define functions: <return type> <name>(<arguments>)
int compute(int x)
{
    // unsigned means no negative values which increases the range of numbers the variable can hold
    const unsigned int FIVE = 5;
    // FIVE = 3; // would throw an error as FIVE is declared constant
    return x * x + FIVE;
}

// the return type for no return value is called 'void'
void playGuessingGame()
{
    // initialize random number seed with time in seconds since the epoch
    srand(time(0));
    // get a random integer between 0 and 9 by doing modulus 10
    int random = std::rand() % 10;
    // need to initialize guess, uninitialized variables are indeterminate
    // meaning it could have any value, even the same as our random one!
    int guess = -1;
    std::cout << "Guess my number between 0 and 9";
    while (guess != random)
    {
        std::cin >> guess;
        if (guess > random)
            std::cout << "Lower";
        else if (guess < random)
            std::cout << "Higher";
        else
            std::cout << "Correct";
    }
}

// the entry point of your program is a function called main which returns an integer
int main()
{
    std::cout << "Hello! Type in a number\n";

    int number;
    std::cin >> number;

    int computed = compute(number);
    std::cout << "I computed x^2+5 as " << computed << "!\n";

    playGuessingGame();

    return 0;
}

// @url: https://repl.it/@MrToph/CPPBasics-Strings
#include <iostream>
// need to import <string> for strings
#include <string>

int main()
{
  // strings are part of the std namespace
  std::string text = "Hello";
  // + is used for concatenation
  text += " World";
  std::cout << text << "\n";
  // length and size are synonyms
  std::cout << text.length() << " " << text.size() << "\n";

  text = text.substr(0, 5);
  for (int i = 0; i < text.length(); i++)
  {
    std::cout << i << ": " << text[i] << "\n";
  }

  // different way to loop over characters
  for (char c : text)
  {
    std::cout << c << "\n";
  }
  return 0;
}

// @url: https://repl.it/@MrToph/CPPBasics-Vectors
#include <iostream>
#include <vector>

int main()
{
    // arrays are defined with [] after the variable name
    // and can be immediately initialized providing values in { ... }
    int arr[] = {1, 2, 3};
    // can specify size in brackets
    // initializes elements in the list, rest to 0
    int brr[3] = {1, 3};
    for (int x : brr)
    {
        // outputs 1, 3, 0
        std::cout << x << "\n";
    }

    std::vector<int> numbers;
    for (int i = 0; i < 3; i++)
    {
        // add a number to the back
        numbers.emplace_back(i);
    }
    // size and accessing vectors is the same as with arrays
    std::cout << "numbers: " << numbers[0] << numbers.size() << "\n";

    // this inserts a number at the second (index 1) place
    numbers.emplace(numbers.begin() + 1, 9);
    // numbers.begin returns an iterator. More on these later
    for (std::vector<int>::iterator it = numbers.begin(); it != numbers.end(); it++)
    {
        // outputs 1, 3, 0
        std::cout << *it << "\n";
    }
}