//student.h
#include<string>
using namespace std;
class Student
{
    public:
        void display();
    private:
        int num;
        string name;
        char sex;
};
//student.cpp
#include<iostream>
#include"student.h"               //提示说这有错 student.h: No such file or directory，本萌新用的devc++，还望各位大佬解决，最好直接写代码，谢谢
void　Student::display()
{
    cout <<"num:"<<num<<endl;
    cout<<"name:"<<name<<endl;
    cout<<"sex:"<<sex<<endl;
}
//main.cpp
#include<iostream>
#include"student.h"
using namespace std;
int main()
{
    Student stud;
    stud.display() ;
    return 0;
}

整合在一起就可以了，DEV里编不了#include"student.h"

#include<iostream>
#include<string>
using namespace std;
class Student
{
    public:
        void display();
    private:
        int num;
        string name;
        char sex;
};
            
void Student::display()
{
    cout <<"num:"<<num<<endl;
    cout<<"name:"<<name<<endl;
    cout<<"sex:"<<sex<<endl;
}
int main()
{
    Student stud;
    stud.display() ;
    return 0;
}

好吧。。。。我还以为教材错了呢