c_cpp CPP - 教程001 - 简介

Posted 2021-05-14

// ---------- C++ Tutorial Example 1 ----------

/* 
 * Multi-line Comment
 */

// These are called preprocessor directives
// They load the files which contain premade functions 
// for your use

// Contains functions for converting from 1 data type to
// another, random number generation, memory management,
// searching, math, sorting and other general purpose functions
#include <cstdlib>

// Provides functions for performing input and output operations
#include <iostream>

// If used you can type cout instead of std::cout
// By using this though you may have conflicts if you define
// functions that share a name with the std namespace
// using namespace std;

// You could define you only want to use part of a namespace like
// using std::cout;
// Which would allow you to use cout instead of std::cout

// Execution of code starts in the main function
// argc and argv is optional data that could be passed
// to the program if it was executed in a terminal
// argc : Number of arguments passed
// argv : Array pointers to strings
int main(int argc, char* argv[]) {
     
    // Outputs the string Hello World to the screen followed by a newline
    // cout is your console or screen
    // << : Stream insertion operator which puts the string
    // into the cout stream to display it
    std::cout << "Hello World" << std::endl;
    
    // If you compile the code into an executable program in the terminal
    // g++ main.cpp
    // And execute it : ./a.out I Love C++
    // You'd see how to work with passed arguments
    
    // If no arguments are passed argc has a value of 1
    // We check that with if to skip printing values if none were passed
    if(argc != 1){
    
        // You can also create a newline with \n
        std::cout << "You entered " << argc << " arguments\n";
    
        // Cycles through all the values in the argc array and prints them
        // We access the values by using their index number starting at
        // 0 
        for(int i = 0; i < argc; ++i){
        
            // We access each string passed by putting its index between []
            // called the subscript operator
            std::cout << argv[i] << "\n";
        }
    }
    
    // When 0 is returned that signals that the program executed without 
    // an error and -1 signals an error occurred 
    return 0;
}

// ---------- End of C++ Tutorial Example 1 ----------

// ---------- C++ Tutorial Example 2 ----------

#include <cstdlib>
#include <iostream>

// Allows you to use the STL string class
#include <string>

// Provides functions to find min and max values
// for data types
#include <limits>

// When we create a variable we are telling the computer
// how much memory to set aside for its value and what
// name we want to associate with that data
    
// Variable names can contain letters, numbers, underscores
// but not math operators, spaces and can't start with a number

// Global variables are declared outside of any functions
// and can be accessed any where in the code
// This is a global integer variable with a name using 
// Hungarian notation
int g_iRandNum = 0;

// const defines constant values that won't change
const double PI = 3.1415926535897932;

int main() {
     
    // Get min and max values for different data types
    
    // bools store true 1, or false 0
    bool bMarried = true;
    
    // char stores 256 single characters represented by your keyboard
    char chMyGrade = 'A';
    
    // unsigned short ints hold values from 0 to 65,535
    // unsigned int & unsigned long int double their max value
    unsigned short int u16Age = 43;
    
    // short ints store between -32,768 to 32,767
    short int siWeight = 180;
    
    // ints range from -2147483648 to 2147483647
    int nDays = 7;
    
    // long ints and long long ints range from -9223372036854775808 to 
    // 9223372036854775807
    long lBigNum = 1000000;
    
    // floats range from 1.17549e-38 to 3.40282e+38
    float fPi = 3.14159;
    
    // Show float precision
    float fBigFloat = 1.1111111111;
    float fBigFloat2 = 1.1111111111;
    float fFloatSum = fBigFloat + fBigFloat2;
    
    // Allows you to print with formatting
    // Float addition has 6 digits of precision
    printf("fFloatSum Precision : %.10f\n", fFloatSum);
    
    // doubles range from 2.22507e-308 to 1.79769e+308
    
    std::cout << "Min double " << 
            std::numeric_limits<double>::min() << "\n";
    std::cout << "Max double " << 
            std::numeric_limits<double>::max() << "\n";
    
    // Show double precision
    double dbBigFloat = 1.11111111111111111111;
    double dbBigFloat2 = 1.11111111111111111111;
    double dbFloatSum = dbBigFloat + dbBigFloat2;
    
    // Allows you to print with formatting
    // Double addition has 15 digits of precision
    printf("dbFloatSum Precision : %.20f\n", dbFloatSum);
    
    // long doubles range from 3.3621e-4932 to 1.18973e+4932
    long double ldPi = 3.1415926535897932;
    
    // You can have the compiler assign a type
    auto whatWillIBe = true;
    
    // SHOW DATA TYPES MIN & MAX VALUES
    
    std::cout << "Min bool " << std::numeric_limits<bool>::min() << "\n";
    std::cout << "Max bool " << std::numeric_limits<bool>::max() << "\n";
    
    std::cout << "Min unsigned short int " << 
            std::numeric_limits<unsigned short int>::min() << "\n";
    std::cout << "Max unsigned short int " << 
            std::numeric_limits<unsigned short int
            >::max() << "\n";
    
    std::cout << "Min short int " << 
            std::numeric_limits<short int>::min() << "\n";
    std::cout << "Max short int " << 
            std::numeric_limits<short int
            >::max() << "\n";

    std::cout << "Min int " << std::numeric_limits<int>::min() << "\n";
    std::cout << "Max int " << std::numeric_limits<int>::max() << "\n";

    std::cout << "Min long " << std::numeric_limits<long int>::min() << "\n";
    std::cout << "Max long " << std::numeric_limits<long int>::max() << "\n";

    std::cout << "Min float " << 
            std::numeric_limits<float>::min() << "\n";
    std::cout << "Max float " << 
            std::numeric_limits<float>::max() << "\n";
    
    std::cout << "Min long double " << 
            std::numeric_limits<long double>::min() << "\n";
    std::cout << "Max long double " << 
            std::numeric_limits<long double>::max() << "\n";
    
    // Get the number of bytes used by a type
    std::cout << "int Size " << sizeof(int) << "\n";
    
    // More about printf()
    // char, int, 5 space right justified int, 
    // 3 decimal float / double, string specifiers
    printf("%c %d %5d %.3f %s\n", 'A', 10, 5, 3.1234, "Hi");
    
    return 0;
}
 
// ---------- End of C++ Tutorial Example 2 ----------

// ---------- C++ Tutorial Example 3 ----------

#include <cstdlib>
#include <iostream>
#include <string>

int main() {
     
    // Create a string
    std::string sQuestion ("Enter Number 1 : ");
    
    // Create empty strings to store values
    std::string sNum1, sNum2;
    
    std::cout << sQuestion;
    
    // Receive user input and store it
    getline(std::cin, sNum1);
    
    std::cout << "Enter Number 2 : ";
    getline(std::cin, sNum2);
    
    // Convert from strings to int
    // std::stod converts from strings to doubles
    int nNum1 = std::stoi(sNum1);
    int nNum2 = std::stoi(sNum2);
    
    // Math Operators
    printf("%d + %d = %d\n", nNum1, nNum2, (nNum1 + nNum2));
    printf("%d - %d = %d\n", nNum1, nNum2, (nNum1 - nNum2));
    printf("%d * %d = %d\n", nNum1, nNum2, (nNum1 * nNum2));
    printf("%d / %d = %d\n", nNum1, nNum2, (nNum1 / nNum2));
    printf("%d %% %d = %d\n", nNum1, nNum2, (nNum1 % nNum2));
    
    // ----- PROBLEM : MILES TO KILOMETERS -----
    // Sample knowing that kilometers = miles * 1.60934
    // Enter Miles : 5
    // 5 miles equals 8.0467 kilometers
    
    // Create needed variables
    std::string sMiles;
    double dMiles, dKilometers;
    
    // Ask user to input miles and store string input
    std::cout << "Enter Miles : ";
    getline(std::cin, sMiles);
    
    // Convert from string to double
    dMiles = std::stod(sMiles);
    
    // Convert from miles to km
    dKilometers = dMiles * 1.60934;
    
    // Output the results
    printf("%.1f miles equals %.4f kilometers\n", dMiles, dKilometers);
    
    // ----- END PROBLEM : MILES TO KILOMETERS -----
    
    return 0;
}

// ---------- End of C++ Tutorial Example 3 —————