Question

当我编译它时说“警告C4700：未初始化的局部变量'计数'使用”。我不知道为什么会这样说，我没有来这里，所以有人可以做我的功课。只是寻找这个错误的帮助，我知道它与函数定义ReadStudentData或Main有关。

感谢

#include<iostream>
#include<fstream>
#include<string>

using namespace std;

struct StudentType
{string studentName;
int testScore;//Between 0 and 100
char grade;


}student[20];

void PrintNameHeader(ostream& out);
bool OpenInputFile(ifstream& inFile, string& infilename ); //OPEN input file
void Pause();// Pause
void ReadStudentData(ifstream& infile, StudentType student[], int& );// Read student infp including first and last name and test score
void AssignGrades(StudentType student[], int);//assign grades to each student
int HighestScore(const StudentType student[], int );//Get the highest scores
void PrintNamesWithHighestScore(const StudentType student[], int);//Print name with highest Scores
void DisplayAllStudents(const StudentType student[], int);//Display all students
void GetLowHighRangeValues(int& , int&);//for example a student types 50 100 , it will get all students within that range
void DisplayStudentsInRange(const StudentType student[], int, int, int);// display students in that range
void SortStudentsByName(StudentType student[], int);// sort students by name
void SortStudentsByScore(StudentType student[], int);// sort students by test score highest to lowest


const int NUM_STUDENTS = 20;

int main()
{

    ifstream infile;
    string inFilename;

    int count = 0;

    StudentType student[NUM_STUDENTS];

    int numStudents;


    PrintNameHeader(cout);

    OpenInputFile(infile,inFilename);

    ReadStudentData(infile, student, numStudents);

    AssignGrades(student, numStudents);

    return 0;
}

//Function definitions

void PrintNameHeader(ostream& out)
{
    //Display name header on screen
    cout << "name" << endl;



}
bool OpenInputFile(ifstream& inFile, string& infilename)
{



    cout << "Enter the name of the .txt file that you want to open for input.\n";
    cout << "Do not put spaces in the file name ";
    cin >> infilename;
    cout << endl;


    inFile.open(infilename.c_str());
    if (inFile.fail())
    {
        cout << "Sorry, the input file " << infilename <<" was not found"<< endl;\
            return false;   
    }

    cout << "Input file " << infilename << " is open for reading.\n\n";
    return true;     
}

void Pause()
{
    cout << endl;

    cin.ignore(80, '\n');

    cout<<"Please hit the enter key to continue...\n";

    cin.get();

}

void ReadStudentData(ifstream& infile, StudentType student[], int& numstudents)
{
    string firstName,
        LastName,
        testScore;

    int count = 0;


    if( infile)

        for (int count; count < NUM_STUDENTS; count++)
        {
            cin >> firstName[count] >> LastName[count] >> testScore[count];

            student[count].studentName = firstName +  ", " + LastName;

        }




        numstudents = count;
        cout << numstudents << endl;




}
void AssignGrades(StudentType student[], int numstudents)
{

    int i;
    for(i=0;i< NUM_STUDENTS;i++)
        switch((int)(student[i].testScore/10))
    {case 10:
    case 9: student[i].grade='A';
        break;
    case 8: student[i].grade='B';
        break;
    case 7: student[i].grade='C';
        break;
    case 6: student[i].grade='D';
        break;
    default: student[i].grade='F';
        break;
    }

}
int HighestScore(const StudentType student[], int numstudents)
{
    int max=0,i;

    for(i=1;i<numstudents;i++)
    {
        if(student[i].testScore>student[max].testScore)
            max=i;
    }

    return max;

}
void PrintNamesWithHighestScore(const StudentType student[], int numstudents)
{

}
void DisplayAllStudents(const StudentType student[], int numstudents)
{

}
void GetLowHighRangeValues(int& lowRange, int& highRange)
{

}

void DisplayStudentsInRange(const StudentType student[], int numStudents, int lownum, int highNum)
{

}

void SortStudentsByName(StudentType student[], int numStudents)
{

}

void SortStudentsByScore(StudentType student[], int numstudents)
{

}

Answer 1

它指的是：

for (int count; count < NUM_STUDENTS; count++)
//   ^^^^^^^^^

您可能需要初始化count，大概是0：

for (int count = 0; count < NUM_STUDENTS; count++)

或者你的意思是使用在外部块中声明的相同count：

for (; count < NUM_STUDENTS; count++)

Answer 2

在for内定义另一个count变量，该变量未初始化。你应该初始化它：

for (int count = 0; count < NUM_STUDENTS; count++)

或在外部范围内需要时删除声明：

for (; count < NUM_STUDENTS; count++)

Answer 3

C和C ++有两个不同的组件来准备变量/对象以供使用。声明和初始化。

这些是声明：

int i;
Object o;
struct Foo;

这些声明的东西，它们不告诉编译器它们应该从哪个值开始。以下是合法的：

int meaning;
if (day == "Thursday")
    meaning = 42;
else
    meaning = 0;

此代码确保始终的含义具有值。

不幸的是，在C和C ++原始类型中，比如整数等，没有好的，安全的默认值。所以如果你写了：

int meaning;
if (day == "Thursday")
    meaning = 42;
else if (day == "Friday")
    meaning = 0;

当天是“星期一”时，“含义”的价值是多少？如果你在考虑一个数字，那你就错了。答案是：它未定义。

编译器将允许您构建这样的代码，但它会提供您看到的错误，以帮助您保护自己。

要同时声明AND初始化变量，只需执行：

int meaning = 0;
if (day == "Thursday")
    meaning = 42;

在您的代码中，问题是：

for (int count; count < NUM_STUDENTS; ++count)

这应该是

for (int count = 0; count < NUM_STUDENTS; ++count)

否则，程序可能会编译，但“count”的初始值可以是-2 ^ 31到+ 2 ^ 31之间的任何数字。

警告C4700：未初始化的局部变量

3 个答案: