C++ 在我的函数中出现错误

Question

需要一些家庭作业帮助。我是 C++ 新手，遇到了一个我不明白的错误。这是我的代码：

/*
 * 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 << "=";
    }
}

错误是“错误：'printLine' 未在此范围内声明”。我确实在 main() 函数中声明了“printLine()”，这还不够吗？或者我是否需要在我计划使用的每个函数中声明函数名？为了回答这个紧迫的问题，我必须在这个最终项目中使用函数。谢谢！！！

Answer 1

假设你真的不想在 main 中声明函数，你要么需要转发声明 welcomeScreen 和 printLine 函数：

#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
}

或者只是在 main 之前定义它们：

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

int printLine(int length) {
    //definition
}

void welcomeScreen() {
    // definition
}

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

Answer 2

你的 printLine 函数只在 main 中声明，所以welcomeScreen 函数看不到它。

您应该将welcomeScreen 和printLine 函数移到main 之前，并确保printLine 在welcomeScreen 之前，这样welcomeScreen 在您尝试调用它之前就知道它存在。

像这样：

/*
 * 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;
}

Answer 3

您在main() 函数的范围内声明了printLine() 函数。 welcomeScreen() 的定义看不到这个声明。

将printLine 的声明移到main 之外和welcomeScreen 之前

welcomeScreen的声明也应该这样做

Answer 4

你的函数没有声明，所以像这样使用它：

/*
 * 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;
}