My ide is showing linter error in the following code. It is highliting yellow in the int main() student s; part
using namespace std;
class student {
public:
int age,DOB;
char name[32];
void getData() {
cin >> age >> DOB >> name;
}
void display() {
cout << name << ends << age << ends << DOB ;
}
};
int main() {
student s;
s.getData();
s.display();
}
and the following code which is same but on adding curlys after student s in the int main student part solves the problem
using namespace std;
class student {
public:
int age,DOB;
char name[32];
void getData() {
cin >> age >> DOB >> name;
}
void display() {
cout << name << ends << age << ends << DOB ;
}
};
int main() {
student s{};
s.getData();
s.display();
}
Your IDE most likely points out that the member variables of s are not initialized.
Using {} syntax ensures that it is initialized.
You can read more about typed of initialization in C++ here.
Your IDE is most likely working with C++ 11.
This method is called as extended initializer lists
This syntax is not required in modern compilers
Try upgrading your IDE to Code blocks 17.12 for C++ codes its very handy!!!
Related
Here the below code is my some part of my program. It doesn't execute it says c++ forbids converting string constants to char*.How can I fix this error?
#include <cstring>
#include <iostream>
using namespace std;
class Bank
{
private:
char name[20];
int acc;
float amount;
public:
Bank()
{
strcpy("",name);
acc = 0;
amount = 0;
}
void open(int a)
{
cout << "Enter name:";
cin >> name;
acc = a;
cout << "Enter Amount" << endl;
cin >> amount;
}
void edit(int flag, float a);
};
int main()
{
Bank B[10];
}
std::strcpy("", name); needs to be std::strcpy(name, "");
Although, setting aside the fact that std::string would be a far better type for name (the future King of England, Charles Mountbatten-Windsor, would not be able to be a customer), writing
name[0] = 0;
would be sufficient.
The program is to take a structure with object name "st" will take age and then first and last name than standard
But it is saying this error
(main.cpp:33:10: error: invalid use of non-static member function ‘void Student::age(int)’)
#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
struct Student{
static string f,l;
static int a,s;
void age(int ag);
void first_name(string fi)
{
f=fi;
}
void last_name(string la)
{
l=la;
}
void standard(int st)
{
s=st;
}
};
void Student :: age( int ag)
{
a=ag;
}
int main() {
Student st;
cin >> st.age >> st.first_name >> st.last_name >> st.standard;
cout << st.age << " " << st.first_name << " " << st.last_name << " " << st.standard;
return 0;
}
Right now it's really unclear what you're trying to achieve with your code.
First of all, your problem is because trying to to put some input into member functions that take arguments, you need to get your input into temporary arguments and pass them, you should also rename your member function to set_age, set_first_name, etc. to indicate what they're doing.
Student st;
int age;
std::string first_name;
std::string last_name;
int standard;
std::cin >> age >> first_name >> last_name >> standard;
st.set_age(age);
st.set_first_name(first_name);
st.set_last_name(last_name);
st.set_standard(standard);
Then you're trying to output them using the same functions without calling them again, but even if you did, they return void, so nothing. You need a different set of member functions to access those variables.
class Student{
int age;
/* rest of the code */
int get_age() const {
return age;
}
};
int main() {
Student student;
student.set_age(10);
std::cout << student.get_age() << '\n';
}
It also looks like you don't know what static means inside a class, right now all your instances of Student class will share age, first_name, last_name and standard, which is probably not what you ment.
I have a project in my C++ class - we're supposed to make a "simple student management system" comprised of a class for the student attribute variables, and a main function with a branch statement that lets the user input names and IDs for the students. I know that I need to use an array to make "slots" for the students, and that my branch statements need to let the user input values into those slots, but I'm not exactly sure how to do it. Here is the code that I have so far.
#include <string>
#include <iostream>
#include <utility>
using std::string;
using std::cin;
using std::cout;
using std::endl;
struct Student {
private:
int id;
string name;
int birthday;
public:
Student()
{
id = 0;
birthday = 0;
}
Student(int id, string name, int birthday)
{
//set your parameters to the class variables
this->id = id;
this->name = name;
this->birthday = birthday;
}
void setID(int id)
{
this->id = id;
}
int getID() {
return id;
}
void setName(string name)
{
this->name = name;
}
string getName()
{
return name;
}
void setBirthday(int birthday)
{
this->birthday = birthday;
}
int getBirthday()
{
return birthday;
}
void output() {
cout << id << name << birthday << endl;
}
};
int main() {
Student arr[50];
cout << "Student Management System" << endl;
cout << "Press 'a' to add a student" << endl;
char a = 1;
int y = 1;
while (a == 'a') {
switch (y)
{
cout << "Input Student ID:";
cin >> id;
}
}
}
What I'm focusing on most is the fourth line from the bottom. I was told that I need to use my setters, so I said that I want what my user inputs to be treated as the value of the ID variable that I set in the class. However, when I wrote this out, I was given an error. Could someone tell me what the issue is?
You should try to get your switch statement working correctly. To use classes setters, you can store the user input to a temporary variable then from your one student you can call the member function. i.e. in your case:
arr[index].setID(tempInputVariable);
There is no id in your main function or as a global variable.
I suggest you overload operator >> to have your structure extract its members from the data stream:
struct Student
{
//...
public:
friend std::istream& operator>>(std::istream& input, Student& s);
};
std::istream& operator>>(std::istream& input, Student& s)
{
input >> s.id;
input >> s.name;
input >> s.birthday;
return input;
}
Although the above code doesn't use setters, it is the preferred method for inputting data.
The overload can be modified to use setters (kind of overkill):
std::istream& operator>>(std::istream& input, Student& s)
{
int id;
input >> id;
s.setID(id);
std::string name;
input >> name;
s.setName(name);
int birthday;
input >> birthday;
s.setBirthday(birthday);
return input;
}
If you don't like the overload, you can perform the steps in your main function:
//...
Student new_student;
//...
{
int student_id;
std::cout << "Input Student ID:";
std::cin >> student_id;
new_student.setID(student_id);
std::string student_name;
std::cout << "Input Student Name: ";
std::cin >> student_name;
new_student.setName(student_name);
int student_birthday;
std::cout << "Input Student Birthday: ";
std::cin >> student_birthday;
new_student.setBirthday(student_birthday);
}
Edit 1: The Database
You'll probably need to store or remember the students. This is easy using the first method above:
std::vector<Student> database;
Student s;
std::cout << "Enter student information (ID, Name and birthday, separated by spaces:\n";
std::cin >> s;
// Append to the database
database.push_back(s);
If you haven't learned std::vector you can try an array:
const size_t MAXIMUM_STUDENTS = 16;
Student database[MAXIMUM_STUDENTS];
size_t database_index = 0;
//...
Student s;
std::cout << "Enter student information (ID, Name and birthday, separated by spaces:\n";
std::cin >> s;
// Append to database
database[database_index] = s;
++database_index;
Hey sorry for the previous Question
OK..My project is to create and run a database for a college using c++
I have to use USN which is a Unique Student Number to access the database :
So i wrote the following program :
#include<iostream>
# include<conio.h>
#include<iomanip>
#include<string.h>
#include<stdlib.h>
int checkinarray(char[],char*);
using namespace std;
class student
{
private :
int sem;
float cgpa;
char password[11];
char passwordtrial[11];
void readdata();
void checkpassword();
void createpassword();
public :
char name[50];
int roll;
void printdata();
char USN[11];
static int number;
void opendatabase();
void firsttime();
public:
student(char n[50]="NONE")
{
number++;
roll=number;
cout<<endl<<"New record under the name of "<<n<<" has been created !"<<endl;
cout<<"Roll number set for new student as : "<<roll<<endl;
cout<<"Use this Roll number for further usage"<<endl<<endl;
};
};
void student::opendatabase()
{
int ch;
cout<<"Enter your name:"<<endl;
cin>>name;
cout<<"Enter your password"<<endl;
cin>>passwordtrial;
if(!strcmp(passwordtrial,password))
{
cout<<"Do you want to read or write";
cin>>ch;
switch(ch)
{
case 0 :
readdata();
break;
case 1 :
printdata();
break;
}
}
else
cout<<"Try Again";
};
void student::readdata()
{
cout <<endl<<"Enter the name of the student : ";
cin >> name;
cout <<endl<<"Enter the semester of the student : ";
cin >> sem;
cout <<endl<<" Enter the cgpa of the student : ";
cin >> cgpa;
};
void student :: printdata()
{
cout << "The name is : " << name << endl;
cout << "The sem is : " << sem << endl;
cout << "The roll is : " << roll << endl;
cout << "The cgpa is : " << cgpa << endl;
}
void student::firsttime()
{
cout<<"Enter your name :";
cin>>name;
cout<<"Hey "<<name<<" Welcome to DBMS "<<endl;
createpassword();
};
void student::createpassword()
{
cout<<"Please enter your 6 character password.. : ";
cin>>password;
cout<<"Please Input your Data here.... :" ;
readdata();
};
int student::number=0;
int main()
{
enum status {existing,newacc,exit};
enum functi{read,update};
char entry1[40];
char entry[10];
char usn[15];
char a[1000][15];
char n[40];
int i,j=0,k;
int s=2;
cout<<endl<<"WELCOME TO COLLEGE NAME"<<endl<<"Press enter to access Database...";
getch();
cout<<endl<<"Welcome to the Main Page of our Database : "<<endl;
while(1)
{//User option
cout<<endl<<"Do you want to access an old entry : "<<endl<<"OR"<<"Create a NEW entry : ";
cin>>entry1;
if(!strcmp(entry1,"old"))
s=existing;
else if(!strcmp(entry1,"new"))
s=newacc;
else
s=exit;
switch(s)
{
case existing:
{
i=1;
break;
}
case newacc:
{ i=1;
cout<<endl<<"Enter your usn : "<<endl;
cin>>usn;
strcpy(a[j],usn);
j++;
strcpy(n,usn);
cout<<n;
student usn(n);
usn.firsttime(); //Start here!! use i to go to next loop or stay in this loop,,change name entry to usn
break;
}
default :{cout<<"Error Input";i=0;break;}
}
if(i)
continue;
cout<<endl<<"What do u want to do??"<<endl<<"Read Entries "<<endl<<"Update entries";
cin>>entry;
if(!strcmp(entry,"read"))
s=read;
else if(!strcmp(entry,"update"))
s=update;
else
s=exit;
cout<<endl<<"Enter your usn : "<<endl;
cin>>usn;
if(checkinarray(a[15],usn))
{
switch(s)
{
case read:{
usn.printdata();
break;
}
case update:{
usn.firsttime();
break;
}
default :
cout<<"Are you sure you want to exit?"<<endl<<"Press 0 to exit"<<endl<<"to back to menu press 1";
cin>>k;
break;
}
if(!k)
break;
}
else cout<<"Invalid Roll number try again!";
}
}
int checkinarray(char a[][15],char b[])
{
int len;
//Finding the length of the string :
len=(sizeof(a)/sizeof(a[0]));
//Checking Conditions for roll number:
for(int k=0;k<len;k++)
{
if(strcmp(a[k],b))
return 1;//stringcompare!!
}
return 0;
}
okay so when i run this i get the following error :
request for member 'printdata' in 'usn', which is of non-class type 'char [15]'
AND
request for member 'firsttime' in 'usn', which is of non-class type 'char [15]'
So please help me overcome this error by suggesting different ways to create and call objects based on user input
OP's problem can be reduced to the following example:
#include<iostream>
#include<string.h>
using namespace std;
class student
{
public:
student(char n[50])
{
}
};
int main()
{
char usn[15];
char n[40];
{
cin >> usn;
strcpy(n, usn);
student usn(n);
}
usn.printdata();
}
This is what is meant by a Minimal, Complete, and Verifiable example. Not everything, but everything needed to reproduce the problem. The beauty of the MCVE is it has reduced the problem to the point where all of it can fit on the screen and probably within the brain, making it easy to analyze and test.
Things to note:
There are two variables named usn
char usn[15];
is an automatic variable within main. It is visible only within main and will expire at the end of main
student usn(n);
is an automatic variable within an anonymous block within main. It is visible only within this block and will expire at the end of the block.
Annotating this block to better explain what is happening, we get
{
cin >> usn; // uses char usn[15];
strcpy(n, usn);
student usn(n); // declares a new variable named usn that replaces char usn[15];for the remainder of this block
} // student usn(n); ends right here and is destroyed.
usn.printdata(); //uses char usn[15]; which has no printdata method.
So how do we fix this?
student usn(n); must have a wider scope.
one of these two variables must change names because once student usn(n); has wider scope it will collide with char usn[15];
Lets give that a quick try.
int main()
{
char usn[15];
char n[40];
student stud(n);
{
cin >> usn;
strcpy(n, usn);
}
stud.printdata();
}
Isn't possible because there is no data in n with which we can make stud. At least not for this minimal example.
int main()
{
char usn[15];
char n[40];
student * stud;
{
cin >> usn;
strcpy(n, usn);
stud = new student(n);
}
stud->printdata();
delete stud;
}
Solves that by dynamically allocating stud so that it is no longer scoped by the braces. Unfortunately that does pick up some extra memory management woes. stud must be deleted. Added a delete, but what if printdata throws an exception and delete stud; is skipped?
int main()
{
char usn[15];
char n[40];
std::unique_ptr<student> stud;
{
cin >> usn;
strcpy(n, usn);
stud.reset(new student(n));
}
stud->printdata();
}
std::unique_ptr takes care of that. But... What about that whole database thing? Why not store stud in a list?
int main()
{
char usn[15];
char n[40];
std::vector<student> studs;
{
cin >> usn;
strcpy(n, usn);
studs.emplace_back(n); // or studs.push_back(student(n));
}
for (student & stud: studs)
{
stud.printdata();
}
}
std::vector solves both problems at once.
I'm quite new with c++ and need some help with the following code.
#include <iostream>
using namespace std;
struct student {
string name;
int age;
float marks;
};
struct student *initiateStudent(string , int , float);
int main ( ) {
int totalStudents = 1;
string name;
int age;
float marks;
cin >> totalStudents;
student *stud[totalStudents];
for( int i = 0; i < totalStudents; i++ ) {
cin >> name >> age >> marks;
stud[i] = initiateStudent(name,age,marks);
}
cout << stud[0]->name;
return 0;
}
struct student *initiateStudent(string name, int age, float marks)
{
student *temp_student;
temp_student->name = name;
temp_student->age = age;
temp_student->marks = marks;
return temp_student;
}
I need in the function initiateStudent return a struct pointer to the pointer array stud by passing the members name, age, marks.
I know that the problem sofar is the fact that temp_student is destroyed when I return to the main file.
So my question is how it could be done by just passing the members of the struct and then return back with information to the pointer array stud.
Thank you very much.
Semi-answer To explain the bad habits:
#include <string>
#include <iostream>
#include <vector>
//using namespace std; often injects subtle bugs. Use with caution
// read more here:
// http://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice
struct student
{
std::string name; // explicit namespacing reduces possibility of unwanted collisions
int age;
float marks;
//added constructor in place of initialization function.
student(std::string name, int age, float marks):name(name), age(age), marks(marks)
{
}
};
int main()
{
int totalStudents = 1;
std::string name;
int age;
float marks;
while (!(std::cin >> totalStudents)) // testing input for success
// Needed extra brackets caught by M.M
// teach me to not test even a throw-away example
{
std::cout << "must... have... good... input..." << std::endl;
cin.clear(); // clear the error and get rid of any other garbage the user may have input.
cin.ignore(numeric_limits<streamsize>::max(), '\n');
}
//student *stud[totalStudents]; illegal in C++
std::vector<student *> stud(totalStudents); // using dynamic array instead
for (int i = 0; i < totalStudents; )// i++ removed
{
if (std::cin >> name >> age >> marks) //testing input
{
stud[i] = new student(name, age, marks); // using constructor
i++; // and put here. Only increment if input is valid.
}
else
{
cin.clear();
cin.ignore(numeric_limits<streamsize>::max(), '\n');
}
}
std::cout << stud[0]->name;
for (student * stu: stud) // cleaning up allocated memory
{
delete stu;
}
return 0;
}
One of the beauties of C++ is you rarely need to self-manage memory. In fact there are huge advantages in not doing it above and beyond not having to clean up after yourself.
#include <string>
#include <iostream>
#include <vector>
struct student
{
std::string name;
int age;
float marks;
student(std::string name, int age, float marks):name(name), age(age), marks(marks)
{
}
};
int main()
{
std::string name;
int age;
float marks;
std::vector<student> stud; // look ma! No pointer!
while (std::cin >> name >> age >> marks) //exits loop on bad input
{
stud.emplace_back(name, age, marks); // building directly in vector
// vector will size itself as needed.
}
std::cout << stud[0].name;
return 0;
}
One more caveat: >> is whiespace delimited. That means it stops when it finds whitespace (space, tab, end of line...) so a name of "John Jacob Jingleheimer-Shmidt" will go into name as "John". >> will then attempt to interpret "Jacob" as age, and that will not go so well.
the simple solution is to make your initiateStudent() creates temp_student on the heap (with new): and returns it. keep in mind heap allocated memory is not freed automatically so don't forget to free it later on yourself.
#include <iostream>
#include <string>
using namespace std;
struct student {
string name;
int age;
float marks;
};
struct student *initiateStudent(string , int , float);
int main ( ) {
int totalStudents = 1;
string name;
int age;
float marks;
cout << "Total student: ";
cin >> totalStudents;
cin.sync(); // very very important to not affect the next input (name)
student* stud = new student[totalStudents];
for( int i = 0; i < totalStudents; i++ )
{
cout << "Name: ";
getline(cin, name);
cin.sync();
cout << "age: ";
cin >> age;
cout << endl;
cout << "Marks: ";
cin >> marks;
cout << endl;
cin.sync();
stud[i] = *initiateStudent(name, age, marks);
}
cout << "Student 1: " << stud[0].name << endl;
delete[] stud;
stud = NULL;
return 0;
}
struct student *initiateStudent(string name, int age, float marks)
{
student *temp_student = new student;
temp_student->name = name;
temp_student->age = age;
temp_student->marks = marks;
return temp_student;
}