如何在C++中使用std :: transform？

Question

我剛剛學習C++，並創建了一個簡單的計算器程序。針對這一點，我有幾個問題：首先，我能做些什麼來清理它，或使它變得更好？其次，在此代碼中，我使用goto語句返回到程序的開頭。我聽說goto被許多程序員看不起，因爲它可以創建「意大利麪條」代碼。有沒有什麼我可以做不使用goto，而是一種什麼樣的？最後，我coppied的代碼從互聯網上一行：

std::transform(returnToMain.begin(), returnToMain.end(), returnToMain.begin(), ::toupper); 

有人能向我解釋這是什麼呢？據我所知，transform和

::toupper 

但不是.begin()和.end()

這裏是我完整的代碼，並感謝大家的幫助：

#include <iostream> 
#include <stdlib.h> 
#include <string> 
#include <cmath> 
#include <algorithm> 
using namespace std; 

void showMenu(); 
unsigned long facInput;             //Prototyping functions 
int getInput(); 
float additionGetInput(); 
float subtractionGetInput(); 
float multiplicationGetInput(); 
float divisionGetInput(); 
unsigned long long factorialInput(unsigned long long facInput); 
float hypotenuseFinder(); 



class prompt               //Class so I don't have to repeatedly type the prompt. 
{ 
public: 
    prompt() 
    { 
     inputPromptOne = "\nEnter float one: "; 
     inputPromptTwo = "\nEnter float two: "; 
    } 
    string inputPromptOne; 
    string inputPromptTwo; 
}; 

string returnToMain; 

prompt prompt; 




int main() 
{ 

    startOfProgram:              //Label for goto function. 
    system("CLS"); 
    showMenu(); 
    int userInput = getInput(); 

    switch(userInput) 
    { 
    case 1:                //Addition 
     system("CLS"); 
     cout << "You chose the Addition Calculator." << endl; 
     cout << "The sum is: " << additionGetInput() << endl; 
     cout << "\n\nEnter 'quit' to return to menu: "; 
     cin >> returnToMain; 
     transform(returnToMain.begin(), returnToMain.end(), returnToMain.begin(), ::toupper); 
     if(returnToMain == "QUIT") 
     { 
      goto startOfProgram; 
     } 

     break; 
    case 2:                 //Subtraction 
     system("CLS"); 
     cout << "You chose the Subtraction Calculator." << endl; 
     cout << "The difference is: " << subtractionGetInput() << endl; 
     cout << "\n\nEnter 'quit' to return to menu: "; 
     cin >> returnToMain; 
     transform(returnToMain.begin(), returnToMain.end(), returnToMain.begin(), ::toupper); 
     if(returnToMain == "QUIT") 
     { 
      goto startOfProgram; 
     } 
     break; 
    case 3:                 //Multiplication 
     system("CLS"); 
     cout << "You chose the Multiplication Calculator." << endl; 
     cout << "The product is: " << multiplicationGetInput() << endl; 
     cout << "\n\nEnter 'quit' to return to menu: "; 
     cin >> returnToMain; 
     transform(returnToMain.begin(), returnToMain.end(), returnToMain.begin(), ::toupper); 
     if(returnToMain == "QUIT") 
     { 
      goto startOfProgram; 
     } 
     break; 
    case 4:                 //Division 
     system("CLS"); 
     cout << "You chose the Division Calculator." << endl; 
     cout << "The quotient is: " << divisionGetInput() << endl; 
     cout << "\n\nEnter 'quit' to return to menu: "; 
     cin >> returnToMain; 
     transform(returnToMain.begin(), returnToMain.end(), returnToMain.begin(), ::toupper); 
     if(returnToMain == "QUIT") 
     { 
      goto startOfProgram; 
     } 
     break; 
    case 5: 
     system("CLS");              //Factorial Finder 
     cout << "You chose the Factorial Calculator." << endl; 
     cout << "Enter a number (MAX 65): "; 
     cin >> facInput; 
     cout << "The factorial is: " << factorialInput(facInput) << endl; 
     cout << "\n\nEnter 'quit' to return to menu: "; 
     cin >> returnToMain; 
     transform(returnToMain.begin(), returnToMain.end(), returnToMain.begin(), ::toupper); 
     if(returnToMain == "QUIT") 
     { 
      goto startOfProgram; 
     } 
     break; 
    case 6:                 //Pythagorean Theorem 
     system("CLS"); 
     cout << "You chose the Pythagorean Theorem Calculator." << endl; 
     cout << "Length of side c (hypotenuse): " << hypotenuseFinder() << endl; 
     cout << "\n\nEnter 'quit' to return to menu: "; 
     cin >> returnToMain; 
     transform(returnToMain.begin(), returnToMain.end(), returnToMain.begin(), ::toupper); 
     if(returnToMain == "QUIT") 
     { 
      goto startOfProgram; 
     } 
     break; 
    default: 
     cout << "That is an invalid function. Try again." << endl; 
     goto startOfProgram; 


    } 

} 
void showMenu() 
{ 
    cout << "1-Addition" << endl; 
    cout << "2-Subtraction" << endl; 
    cout << "3-Multiplication" << endl; 
    cout << "4-Division" << endl; 
    cout << "5-Factorial" << endl; 
    cout << "6-Pythagorean Theorem" << endl; 
    cout << "---------------------" << endl; 
} 
int getInput() 
{ 
    int userInput; 

    cout << "Choose a function: "; 
    cin >> userInput; 
    return userInput; 
} 
float additionGetInput() 
{ 
    float addInput1; 
    float addInput2; 

    cout << prompt.inputPromptOne; 
    cin >> addInput1; 
    cout << prompt.inputPromptTwo; 
    cin >> addInput2; 
    system("CLS"); 

    float sum = addInput1 + addInput2; 
    return sum; 
} 
float subtractionGetInput() 
{ 
    float subInput1; 
    float subInput2; 

    cout << prompt.inputPromptOne; 
    cin >> subInput1; 
    cout << prompt.inputPromptTwo; 
    cin >> subInput2; 
    system("CLS"); 

    float difference = subInput1 - subInput2; 
    return difference; 
} 
float multiplicationGetInput() 
{ 
    float mulInput1; 
    float mulInput2; 

    cout << prompt.inputPromptOne; 
    cin >> mulInput1; 
    cout << prompt.inputPromptTwo; 
    cin >> mulInput2; 
    system("CLS"); 

    float product = mulInput1 * mulInput2; 
    return product; 
} 
float divisionGetInput() 
{ 
    float divInput1; 
    float divInput2; 

    cout << prompt.inputPromptOne; 
    cin >> divInput1; 
    cout << prompt.inputPromptTwo; 
    cin >> divInput2; 
    system("CLS"); 

    float quotient = divInput1/divInput2; 
    return quotient; 
} 
unsigned long long factorialInput(unsigned long long facInput) 
{ 
    if(facInput==1) 
    {cout << "---------------------" << endl; 
     return 1; 
    } 
    else 
    { 
     return facInput*factorialInput(facInput-1); 
    } 
} 
float hypotenuseFinder() 
{ 
    float a; 
    float b; 

    cout << "Enter length of side a: "; 
    cin >> a; 
    cout << "\nEnter length of side b: "; 
    cin >> b; 

    float hypotenuse = sqrt(pow(a, 2) + pow(b, 2)); 
    return hypotenuse; 
} 

Answer 1

的begin和end方法是從C++ STL迭代器API。在<algorithm>庫中使用C++迭代器

std::string input = "Yo Dogg"; 
std::string output(input); 
std::transform(input.begin(), input.end(), 
       output.begin(), 
      [](auto character) { 
    return ::toupper(character); 
}); 
/// 'output' will contain "YO DOGG" 

...大部分功能：

複製可以更清晰（和較少最佳）的例子，像這樣（running example on ideone）lambda表達式表示。