I am trying string comparision using operator overloading i am using > operator , i am not getting the correct output, can you tell me what mistake i am doing here is my code
#include<iostream.h>
#include<stdio.h>
#include<string.h>
#include<conio.h>
class strclass
{
public:
char s1[20];
void getdata()
{
cin>>s1;
}
void showdata()
{
cout<<s1;
}
int operator>(strclass obj)
{
int temp,temp1;
temp=strlen(s1);
temp1=strlen(obj.s1);
if(temp>temp1)
{
return 1;
}
else
return 0;
}
};
void main()
{
clrscr();
strclass obj1,obj2;
int temp3;
if(obj1>obj2)
{
cout<<"string 1 is greater";
}
else
{
cout<<"string 2 is greater";
}
cout<<"enter string 1"<<endl;
obj1.getdata();
// obj1.showdata();
cout<<"enter string 2"<<endl;
obj2.getdata();
// obj2.showdata();
getch();
}
I am using basic library functions. Thanks!
You need to put the data before comparing the strings
The operator should return an int
For your class, with a public s1 member, you should use a free function for the comparison operator, which increases encapsulation, of the form bool operator<(strclass s1, strclass s2) instead of a member function
Related
I'm new to c++ because all throughout our lab activities we just use C# and I'm still trying get the gist of it. So our last lab, which uses c++, is to show our genealogy-our family tree- and my problem right now is printing. Can someone point out what's wrong in my function or why it's not printing and what's the best way to do it?
#include <iostream>
#include <string>
using namespace std;
class parent
{
public:
void setMom(string mom)
{
mother=mom;
}
void setDad(string dad)
{
father=dad;
}
string getDad(void)
{
return father;
}
string getMom(void)
{
return mother;
}
protected:
string mother;
string father;
};
class Member: public parent
{
public:
string name;
Member()
{
}
void setName(string kid)
{
name=kid;
}
void setStatus(string stat)
{
status=stat;
}
void setAge(int num)
{
age=num;
}
string getName()
{
return name;
}
private:
string status;
int age;
};
char addPerson()
{
Member person;
char mom[50];
char dad[50];
char kid[50];
char stat[7];
int num;
cout<<"Name: ";
cin>>kid;
person.setName(kid);
cout<<"Age: ";
cin>>num;
person.setAge(num);
cout<<"Status(Living/Diseased): ";
cin>>stat;
person.setStatus(stat);
cout<<"Father: ";
cin>>dad;
person.setDad(dad);
cout<<"Mother: ";
cin>>mom;
person.setMom(mom);
}
my function for printing.
void showme()
{
Member person;
cout<<person.getMom();
}
//-----------------------------------------------------MAIN--------------------------------------------------
int main()
{
while(1)
{
int choice;
cout<<" 1. Add member"<<"\n";
cout<<" 2. Edit member"<<"\n";
cout<<" 3. Show family tree"<<"\n";
cout<<" 4. Exit"<<"\n";
cin>>choice;
if(choice==1)
{
addPerson();
}
else if(choice==2)
{
}
else if(choice==3)
{
showme();
}
else if(choice==4)
{
break;
}
}
}
I use for_each and mem_fun_ref as a example ,but there are some error in compile ,what's the problem
#include<iostream>
#include<algorithm>
#include<set>
#include<iterator>
using namespace std;
class Tst
{
public:
Tst(int a, string b):n(a),s(b)
{}
bool operator<(const Tst& t)const
{
return this->n < t.n;
}
int GetN()const
{
return n;
}
string GetS()const
{
return s;
}
void SetN(int a)
{
n = a;
}
void SetName(string name)
{
s = name;
}
void Print(void)
{
cout <<"n is:" << n <<"\ts is:" << s << endl;
}
private:
int n;
string s;
};
int main(void)
{
typedef set<Tst> TstSet;
TstSet tst;
tst.insert(Tst(10, "abc"));
tst.insert(Tst(1, "def"));
for_each(tst.begin(), tst.end(), mem_fun_ref(&Tst::Print));
return true;
}
:4200: 错误：对‘(std::mem_fun_ref_t) (const Tst&)’的调用没有匹配，是什么原因
std::set's contained objects are const, so you can only call const functions on them. Your Print function should be marked const.
The function should be const, because std::set only works with const objects
void Print(void)const
{
}
I have class Pstring
class Pstring
{
private:
string palindrome;
public:
Pstring() { palindrome = ""; }
Pstring(string pal) { setString(pal); }
void setString(string pal) { palindrome = pal; }
string getPal() const { return palindrome; }
};
an object in my main method Pstring palindrome(palin) defined by
string palin = "";
cout << "Enter a palindrome:\n";
getline(cin, palin);
Pstring palindrome(palin);
and a current test method bool isPalindrome(string pal)defined as
bool isPalindrome(string pal)
{
bool flag;
cout << "Do I have access to this?";
cout << pal;
//code goes here to check for palindrome, return bool
}
I want to have my Pstring class object palindrome use the method isPalindrome in main, but when I try and invoke the method by using palindrome.isPalinedrome(palin); it doesn't seem to have access to the method.
What can I do to allow a method outside the class to be used by a class object in main?
You don't have a isPalinedrome() method defined in the Pstring class, so you can't call it as palindrome.isPalinedrome() in your main code.
Instead of having Pstring try to call a function in your main code, you should move the palindrome logic into Pstring, and then the main code can ask Pstring when needed.
Try this:
class Pstring
{
private:
string value;
public:
Pstring() { }
Pstring(const string &s) { setString(s); }
void setString(const string &s) { value = s; }
string getString() const { return value; }
// add this...
bool isPalindrome() const {
//code goes here to check value for palindrome, return bool
}
};
Then your main code can do this:
bool isPalindrome(const string &value)
{
Pstring palindrome(value);
return palindrome.isPalindrome();
// or simply:
// return Pstring(value).isPalindrome();
}
int main()
{
string palin;
cout << "Enter a palindrome:\n";
getline(cin, palin);
if (isPalindrome(palin)) {
// do something ...
} else {
// do something else...
}
return 0;
}
Or this:
int main()
{
string palin;
cout << "Enter a palindrome:\n";
getline(cin, palin);
Pstring palindrome(palin);
if (palindrome.isPalindrome()) {
// do something ...
} else {
// do something else...
}
return 0;
}
You should add your test method into the class:
class Pstring
{
private:
string palindrome;
public:
// you don't need to initialize palindrome = "" (it's initialized by default)
Pstring() {}
// always pass strings as const reference unless you have
// special reason to do it another way...
Pstring(const string& pal) { setString(pal); }
void setString(const string& pal) { palindrome = pal; }
string getPal() const { return palindrome; }
bool isPalindrome() const // you don't have to pass string
{
bool flag;
cout << "Do I have access to this?";
cout << palindrome; // please note this
//code goes here to check for palindrome, return bool
}
};
And also please note the typo:
palindrome.isPalinedrome(palin);
You can use function pointer to implement it:
declare class:
class Pstring{
private:
string palindrome;
public:
Pstring() { palindrome = ""; }
Pstring(string pal) { setString(pal); }
void setString(string pal) { palindrome = pal; }
string getPal() const { return palindrome; }
//add a function pointer member:
bool(*isPalindrome) (string);
};
then define function:
bool isPalindrome(string pal)
{
bool flag;
cout << "Do I have access to this?";
cout << pal;
//code goes here to check for palindrome, return bool
return true;
}
now you can write code in main function:
string palin = "";
cout << "Enter a palindrome:\n";
getline(cin, palin);
Pstring palindrome(palin);
palindrome.isPalindrome = isPalindrome;//bind function
you can use the function by the object now:
palindrome.isPalindrome(palin);
Sorry. what's the point to create this class? the only thing you need is the helper function isPalindrome(const std::string&). If you need some kinda scope protection, put it into a namespace may look better
Sorry but I have to say you are just make things complicated.
C++ is not java. If you don't use it, you should not pay for it.
I don't know how to call my class functions into printData(Testscore&) and readData(TestScore).
Also, could someone tell me why my Average() isn't being called to the main? I just learned about using static member variables and static member functions and was wondering if I am using them incorrectly.
The readData function:
Does not use copy constructor.
Reads all instance variables like the student's names and all their
grades.
Uses functions to store the variables, name, element of each grade of array pointed to private pquiz, and static member
grades of how many grades to read.
The printData function:
Writes the name and average grade of the quizzes.
Uses copy constructor.
This is my program so far:
#include <iostream>
#include <string>
using namespace std;
class TestScore {
private:
static int grades;
string name;
double *pquiz;
double average;
public:
TestScore();
~TestScore();
void setName(string);
static void setGrades(int);
void setPquiz(double *);
void setAverage(double);
string getName();
static int getGrades();
double getPquiz();
void readData(TestScore &);
void printData(TestScore);
double Average(double *, int);
static void Grade(int);
};
TestScore::TestScore() {
name="";
pquiz=new double[grades];
average=0;
}
void TestScore::setName(string name1) {
if(name1!="1") {
name=name1;
}
}
void TestScore::setPquiz(double *pquiz1) {
if(pquiz>=0) {
pquiz=pquiz1;
}
}
void TestScore::setGrades(int grades1) {
if(grades1>=0) {
grades=grades1;
}
}
void TestScore::setAverage(double average1) {
if(average1>=0) {
average=average1;
}
}
string TestScore::getName() {
return name;
}
int TestScore::getGrades() {
return grades;
}
double TestScore::getPquiz() {
return *pquiz;
}
double Average(double *pquiz, int grade) {
int count;
double total=0;
double average=0;
for(count=0; count<grade; count++) {
total+=pquiz[count];
}
average=total/grade;
return average;
}
void readData(TestScore&) {
}
void printData(TestScore) {
}
TestScore::~TestScore() {
delete [] pquiz;
pquiz=0;
}
int TestScore::grades=0;
void TestScore::Grade(int a) {
grades+=a;
}
int main() {
const int grades = 3;
const int students = 4;
TestScore exam;
string student;
int grade;
double *pquiz;
double average;
for(int i=0; i<students; i++) {
cout<<"Student "<<(i+1)<<": ";
cin>>student;
exam.setName(student);
cout<<endl;
for(int count=0; count<grades; count++) {
cout<<"Quiz "<<(count+1)<<": ";
cin>>pquiz[count];
exam.setPquiz(pquiz);
exam.getPquiz();
while(pquiz[count]<0) {
cout<<"Error, invalid test score, please try again."<<endl;
cout<<"Quiz "<<(count+1)<<": ";
cin>>pquiz[count];
}
}
exam.setAverage(average);
cout<<exam.getName()<<" average is "<<Average(pquiz, grade)<<endl<<endl;
}
readData(exam);
printData(exam);
return 0;
}
Don't use static anywhere, at least not for now. You have too many variables of the same name, scattered all over the place. Try to clean them up.
TestScore::TestScore()
{
name = "";
//pquiz = new double[grades];//#grades is undefined
pquiz = NULL;
average = 0;
}
grades is not defined yet, it could be zero, or it could be -817. You should just remove that line, or you can put something like pquiz = new double[10] that's if you are sure the number of quiz will not exceed 10.
TestScore::~TestScore()
{
if (pquiz) delete[] pquiz;
pquiz = NULL;
}
delete pquiz only if it is not NULL
int main() {
const int grades = 3;
const int students = 4;
TestScore exam;
string student;
int grade;
double *pquiz;
...
This is a different pquiz, it is a pointer which points to nothing, it doesn't really exist, you can't use it like that.
in my school assignment i need a small help
this is my header file:
#include <iostream>
#include <cstring>
using namespace std;
#include "ISBNPrefix.h"
class ISBN
{
char str[11];
char area[6];
char publisher[8];
char title[7];
bool registered;
public:
ISBN();
ISBN(const char*,ISBNPrefix &);
void toStr(char*)const;
void toStrWithStyle(char*)const;
bool empty()const;
bool isRegistered() const;
bool read(istream& is, const ISBNPrefix& list);
void display(ostream&) const;
};
int isValid(const char* str);
and this is the implementation of my file:
#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include <iomanip>
using namespace std;
#include "ISBN.h"
ISBN::ISBN()
{
str[0]='\0';
area[0]='\0';
publisher[0]='\0';
title[0]='\0';
registered=false;
}
ISBN::ISBN(const char* s,ISBNPrefix& p)
{
if(isValid(s)==1)
{
strcpy_s(str,s);
}
else
{
*this=ISBN();
}
}
bool ISBN::empty()const
{
bool chk=false;
if(str[0]=='\0')
chk=true;
return chk;
}
void ISBN::toStrWithStyle(char* s) const
{
if(registered)
{
sprintf(s,"%s-%s-%s-%c",area,publisher,title,str[9]);
}
else
{
toStr(s);
}
}
void ISBN::toStr(char* s) const
{
if (str[0]!='\0')
strcpy(s,str);
else
strcpy(s,"no data");
}
void ISBN::display(ostream & os) const
{
char str[14];
toStrWithStyle(str);
cout<< setw (13) <<str;
}
int isValid(const char* str)
{
int rc=0;
if(str!=0)
{
int sum,i=0;
sum=0;
for(i=0;i<10;i++)
sum+=(str[i]-'0')*(10-i);
if(sum%11==0)
{
rc= 1;
}
}
else
rc=0;
return rc;
}
bool ISBN::read(istream& is, const ISBNPrefix& list)
{
char str[11];
bool quit=false;
bool ok=false;
char lists;
do{
cout<<"ISBN (0 to quit) : ";
is.getline(str,11); //or is.get(str,11)
if(strcmp(str,"0")==0)
quit=true;
else if (isValid(str)==1)
{
*this=ISBN(str,list);
ok=true;
cout<<"isbn is valid"<<endl;
}
else
{
*this=ISBN();
cout<<"invalid ISBN"<<endl;
}
} while(!quit&&!ok);
return !quit;
}
in the ISBN::read where I say
*this=ISBN(str,list);
i want to overload another member but i can't.
can anyone tell me how can i do that?
First I would suggest use std::string in favour of char[]. It will save a lot of trouble. For reading ISBN I would write something like this:
bool ISBN::read(istream& is)
{
ISBN result;
// reading into result
std::swap(*this,result);
return !quit;
}
Or even better (as a non member function):
std::istream& operator>>(istream& is, ISBN& obj)
{
ISBN result;
// reading into result
is(!quit)
is.clear(std::ios_base::failbit);
std::swap(obj,result);
return is;
}
In any way you should RAII classes for your resources. In your special case std::string instead of char[].