C++通過我的功能獲取錯誤

Question

需要一些家庭作業幫助。我是C++的新手，並且遇到了一個我不明白的錯誤。這裏是我的代碼：

/* 
* homework6.cpp 
* Coder: omega9380 
* Final Project 
*/ 

#include <iostream> 
#include <string> 
#include <iomanip> 
using namespace std; 

int main() { 

    void welcomeScreen(); 
    void printLine(int length); 

    welcomeScreen(); 

    return 0; 
} 

void welcomeScreen() { 
    string userName = ""; 
    string title1 = "CMPSC101 FINAL PROJECT"; 
    string title2 = "CREATED BY: OMEGA9380"; 

    // Welcome screen: 

    system("CLS"); 

    cout << "/"; 
    printLine(80); 
    cout << "\\" << endl; 
    cout << "|" << setw(81) << "|" << endl; 
    cout << "|" << setw(41 + (title1.length()/2)) << title1 << setw(40 - (title1.length()/2)) << "|" << endl; 
    cout << "|" << setw(41 + (title2.length()/2)) << title2 << setw(40 - (title2.length()/2)) << "|" << endl; 
    cout << "|" << setw(81) << "|" << endl; 
    cout << "\\"; 
    printLine(80); 
    cout << "/" << endl; 
} 

void printLine(int length) { 
    for (int i = 0; i < length; i++) { 
     cout << "="; 
    } 
} 

錯誤是「error：'printLine'未在此範圍內聲明」。我在main（）函數中聲明瞭「printLine（）」，這還不夠嗎？還是我需要在每一個我打算使用它的函數中聲明函數名？爲了回答這個棘手的問題，我必須在這個最終的項目中使用函數。謝謝！！！

Answer 1

聲明做假設你真的不希望在主已經宣佈功能，你要麼需要向前聲明welcomeScreen和打印線功能：

#include <iostream> 
#include <string> 
#include <iomanip> 
using namespace std; 

int printLine(int); 
void welcomeScreen(); 

int main() { 
    welcomeScreen(); 
    return 0; 
} 

void welcomeScreen() { 
    // definition 
} 

void printLine(int length) { 
    // definition 
} 

或之前主只是定義它們：

#include <iostream> 
#include <string> 
#include <iomanip> 
using namespace std; 

int printLine(int length) { 
    //definition 
} 

void welcomeScreen() { 
    // definition 
} 

int main() { 
    welcomeScreen(); 
    return 0; 
} 

Answer 2

你不有申報爲你的功能，因此使用它是這樣的：

/* 
* homework6.cpp 
* Coder: omega9380 
* Final Project 
*/ 

#include <iostream> 
#include <string> 
#include <iomanip> 
using namespace std; 

void welcomeScreen() { 
    string userName = ""; 
    string title1 = "CMPSC101 FINAL PROJECT"; 
    string title2 = "CREATED BY: OMEGA9380"; 

    // Welcome screen: 

    system("CLS"); 

    cout << "/"; 
    printLine(80); 
    cout << "\\" << endl; 
    cout << "|" << setw(81) << "|" << endl; 
    cout << "|" << setw(41 + (title1.length()/2)) << title1 << setw(40 - (title1.length()/2)) << "|" << endl; 
    cout << "|" << setw(41 + (title2.length()/2)) << title2 << setw(40 - (title2.length()/2)) << "|" << endl; 
    cout << "|" << setw(81) << "|" << endl; 
    cout << "\\"; 
    printLine(80); 
    cout << "/" << endl; 
} 

void printLine(int length) { 
    for (int i = 0; i < length; i++) { 
     cout << "="; 
    } 
} 

int main() { 

    void welcomeScreen(); 
    void printLine(int length); 

    welcomeScreen(); 

    return 0; 
} 

Answer 3

您聲明main()功能的範圍內printLine()功能。 welcomeScreen()的定義沒有看到該聲明。

移動printLine之外的聲明main和welcomeScreen

之前同樣應與welcomeScreen

Answer 4

您的printLine函數只在main中聲明，所以welcomeScreen函數看不到它。

您應該在main之前移動welcomeScreen和printLine函數，並確保printLine在welcomeScreen之前，以便welcomeScreen在嘗試調用它之前知道它存在。

像這樣：

/* 
* homework6.cpp 
* Coder: omega9380 
* Final Project 
*/ 

#include <iostream> 
#include <string> 
#include <iomanip> 
using namespace std; 

void printLine(int length) { 
    for (int i = 0; i < length; i++) { 
     cout << "="; 
    } 
} 

void welcomeScreen(void) { 
    string userName = ""; 
    string title1 = "CMPSC101 FINAL PROJECT"; 
    string title2 = "CREATED BY: OMEGA9380"; 

    // Welcome screen: 

    system("CLS"); 

    cout << "/"; 
    printLine(80); 
    cout << "\\" << endl; 
    cout << "|" << setw(81) << "|" << endl; 
    cout << "|" << setw(41 + (title1.length()/2)) << title1 << setw(40 - (title1.length()/2)) << "|" << endl; 
    cout << "|" << setw(41 + (title2.length()/2)) << title2 << setw(40 - (title2.length()/2)) << "|" << endl; 
    cout << "|" << setw(81) << "|" << endl; 
    cout << "\\"; 
    printLine(80); 
    cout << "/" << endl; 
} 

int main() { 

    welcomeScreen(); 

    return 0; 
}