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In my code I am trying to make loop that works by changing pointer target and printing value of the same pointer. This code is my method for infinite list.
#include <iostream>
using namespace std;
class pacjent
{
public:
char nazwisko[20];
pacjent*nastepny;
pacjent();
~pacjent();
};
pacjent *POCZATEK = NULL, *KONIEC = NULL;
pacjent::pacjent() {
cout << "Podaj nazwisko: ";
cin >> nazwisko;
if (POCZATEK == NULL) {
POCZATEK = this;
KONIEC = this;
} else {
KONIEC->nastepny = this;
nastepny = NULL;
}
}
pacjent::~pacjent() {
POCZATEK = POCZATEK->nastepny;
}
pacjent* NOW = POCZATEK;
void drukuj() {
///////////////////////////////// LOOP MENTIONED
// while(NOW->nastepny!=NULL)
// {
cout << NOW->nazwisko << endl; //do not work
// NOW=NOW->nastepny;
// cout << POCZATEK->nazwisko << endl; // works fine
// }
} //////////////////////////////////
int main() {
char SELECTOR;
while (SELECTOR != 'q') {
cin >> SELECTOR;
switch (SELECTOR) {
case 'n':
KONIEC = new pacjent;
break;
case 'p':
delete POCZATEK;
break;
case 'd':
drukuj();
break;
default:
break;
}
}
return 0;
}
The function drukuj() won't print content of 'NOW' (I get empty screen) pointer but with POCZATEK works fine. Any ideas?
The function drukuj() won't print content of 'NOW' (I get empty screen) pointer but with POCZATEK works fine. Any ideas?
NOW is initialized as:
pacjent* NOW = POCZATEK;
At that time, the value of POCZATEK is NULL. Hence, NOW also gets initialized to NULL. Later on in your code, POCZATEK is changed to point to newly created objects but that does not change where NOW points to. It still points to NULL.
You can make sure NOW and POCZATEK always point to the same object by making NOW a reference to a pointer and initialize it with POCZATEK.
pacjent*& NOW = POCZATEK;
pacjent* NOW = POCZATEK; // this is null
Create new pacjent object and assign it's members the values you want then try to print out.
Related
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Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
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I am fairly new to c++. I am trying to add another element in the array. The function should change the array and the number of items in the array after the addEntry function is completed, but it doesn't. If I use the display function to show the array, only the original array is shown. Please help.
#include<iostream>
#include<string>
using namespace std;
const int MAXSIZE = 10; // total size of array
void display(string[], int);
void addEntry(string[], int&);
int main()
{
string name[MAXSIZE] = {"raj","casey","tom","phil"};
int numEntries = 4; // number of elements in the array
string choice; // the user choice to add an element or display or exit
cout<<numEntries<<" names were read in."<<endl;
do
{
cout<<endl<<"Enter menu choice (display, add, quit): ";
getline(cin,choice);
if (choice == "display")
{
display(name, numEntries);
cout<<endl;
}
else if (choice == "add")
{
addEntry(name, numEntries);
cout<<endl;
}
else
{
cout<<"bye"<<endl;
}
} while (choice!="quit");
system ("pause");
return 0;
}
void display(string name[], int numEntries)
{
for (int i = 0; i < numEntries; i++)
{
cout<<name[i]<<endl;
}
return;
}
void addEntry(string name[], int& numEntries)
{
if (numEntries<MAXSIZE-1)
{
numEntries++;
cout<<"Enter name of the person to add: ";
getline(cin,name[numEntries]);
cout << "Entry added.";
return;
}
else
{
cout<<"There is not enough space is in the array to add a new entry!";
return;
}
}
getline(cin,name[numEntries]);
numEntries is the number of valid entries in your array. name[numEntries] is the element that is following the last valid entry. Use name[numEntries-1].
Or even better, use std::vector instead of C arrays, after all, you are writing in C++.
Your program works, you are just pointing the the wrong location in your array in addEntry. Remember that arrays in C++ are 0-based, try incrementing the value of numEntries AFTER inserting the element in your array, for example:
void addEntry(string name[], int& numEntries)
{
if (numEntries<MAXSIZE)
{
cout<<"Enter name of the person to add: ";
getline(cin,name[numEntries++]);
cout << "Entry added.";
return;
}
else
{
cout<<"There is not enough space is in the array to add a new entry!";
return;
}
}
The bug in your code is in the following lines:
numEntries++;
cout<<"Enter name of the person to add: ";
getline(cin,name[numEntries]);
You need to increment numEntries after the call to getline. Use:
cout<<"Enter name of the person to add: ";
if ( getline(cin,name[numEntries]) )
{
// Increment only if getline was successful.
numEntries++;
}
I implemented a Quiz Code and did a short change at the end of it to check if the User answered it correctly.
My if / else looks like this:
if (answer == rightanswer){
rightA = true;
}
else {
rightA = false;
}
return rightA;
I already checked with the debugger that if the correct answer is entered it goes to rightA = true; and to return, so this works finde.
But if i check the value of rightA it's false.
If it's needed, here is the function that i use to call the Quiz:
void gameOver(char field[HEIGHT][WIDTH], char newField[HEIGHT][WIDTH]){ // TODO
bool rightA = false;
showQuizDialog(rightA);
do{
system("cmd /c cls");
switch (rightA){
case true : cout << "menu"; menu(field, newField); break;
case false : showQuizDialog(rightA); break;
default : cout << " ";
}
}while(rightA == false);
}
I'm a bit hintless. I may have some logic failure in it i just don't see at the moment.
Greetings
E: I don't wanted to bomb you guys with code. But here is it:
bool showQuizDialog(bool rightA){
Quiz* quiz = Quiz::getInstance();
quiz -> askQuestion(rightA);
return rightA;
}
And the full askQuestion:
bool Quiz::askQuestion(bool rightA) {
int fragenID = rand() % this->fragen.size(); //zufällige Fragen auswählen
struct Question frage = this->fragen.at(fragenID);
std::cout << frage.frage.c_str() << std::endl << endl; //Frage stellen
int rightanswer = this->listAnswers(frage.antworten);
int answer = this->readAnswer(0, frage.antworten.size() - 1);
if (answer == rightanswer){
rightA = true;
}
else {
rightA = false;
}
return rightA;
}
Is showQuizDialog(rightA) supposed to magically change the value of rightA? (I'm assuming you're not passing it by reference).
Did you mean to write rightA = showQuizDialog(rightA) or rightA = quiz -> askQuestion(rightA)?
Also, in your switch that switches on a bool, do you expect any other values than a true or a false?
Your showQuizDIalog is a call-by-value function. So always store the return value of the function into rightA, when calling showQuizDialog, that is :
rightA = showQuizDialog(rightA);
Otherwise, change your function declaration to allow pass-by-reference, maybe like this
showQuizDialog(&rightA);
and no need to return anything from the function(just use a pointer instead of a variable rightA inside the function)
struct stack_struct
{
int number;
struct stack_struct *next_number;
};
stack_struct *mainStruct;
class stack_class
{
private:
struct stack_struct *head;
public:
stack_class();
//~stack_class();
void pushNumber(int number);
void popANumber();
void findNumber();
void clearStack();
void sizeFinder();
void printStack();
};
stack_struct *pointerFunc,*pointerFunc2,*pointerFunc3,*printPointer;
stack_class::stack_class()
{
head=NULL;
}
void stack_class::pushNumber(int numberFunc)
{
if(head==NULL)
{
head = new stack_struct;
head->number = numberFunc;
head->next_number = NULL;
pointerFunc2=head;
}
else
{
pointerFunc = new stack_struct;
pointerFunc->number=numberFunc;
pointerFunc->next_number=NULL;
head->next_number=pointerFunc;
head=pointerFunc;
}
}
void stack_class::printStack()
{
while(pointerFunc2)
{
cout<<pointerFunc2->number<<endl;
pointerFunc2=pointerFunc2->next_number;
}
}
int optionChosen;
int main()
{
stack_class mainClassStack;
do
{
cin>>optionChosen;
switch(optionChosen)
{
case 1:
{
int pushInt;
cout<<"\n\nEnter Number: ";
cin >> pushInt;
mainClassStack.pushNumber(pushInt);
break;
}
case 2:
{
break;
}
case 3:
{
break;
}
case 4:
{
break;
}
case 5:
{
break;
}
case 6://print
{
mainClassStack.printStack();
break;
}
default:
{
break;
}
}
}while(optionChosen!=7);
return 0;
I am trying to implement a stack type of data list using dynamic memory (linked list). But when I try to prints the list, it only prints the list once, and if I try to reprint again using option 6, its like the list is gone. I went over the code twice but couldnt figure out what the problem was. Any suggestions?
The problem with your code is that after you print the stack, you aren't resetting pointerFunc2 to become head.
Either reset it correctly, or use a local variable inside your print function.
Here's a corrected version of your function:
void stack_class::printStack()
{
while (pointerFunc2)
{
cout << pointerFunc2->number << endl;
pointerFunc2 = pointerFunc2->next_number;
}
// reset pointerFunc2 so the next iteration
// can start at the head and print again.
pointerFunc2 = head;
}
The problem is when you print the stack the first time with this
pointerFunc2=pointerFunc2->next_number;
the pointerFunc2 becomes the last element after the first iteration. So that's why you think its gone. You should reset pointerFunc2 to point to the head node after being printed. So save it first, then after iterating thru the whole list, restore it, so that the next time you print the stack you will start with the head node.
The reason the second print does not work is that you are using a global variable instead of a local one:
stack_struct *pointerFunc2;
When you declare a variable outside a function or a class, it becomes global variable. Global variables survive function invocations, and retain the value that was last set into them. In order to be local, a variable needs to be declared inside printStack, initialized to the stack's head, and then discarded upon exiting the function. The same is true about pointerFunc.
The printPointer and pointerFunc3 variables are unused, and can be removed from the source code.
I'm getting some weird behavior with a vector in C++ I was hoping someone could help me out. I have a vector like so:
vector<Instruction*> allInstrs;
the struct for Instruction is as follows:
struct Instruction : simple_instr
{
InstrType type;
Instruction(const simple_instr& simple) : simple_instr(simple)
{
type = Simple;
loopHeader = false;
loopTail = false;
}
int Id;
bool loopHeader;
bool loopTail;
};
the problem I'm having is this:
I need to iterate through each instruction and pull out specific fields and use those to do some analysis on the instructions in the vector. To do that, I was basically doing
VariableList Variables;
void GenerateVariableList()
{
for (int i = 0; i < allInstrs.size(); i++)
{
Variables.Add(allInstrs[i]);
}
Variables.RemoveDuplicates();
}
Variable List is defined as
struct VariableList
{
void Add(simple_instr* instr)
{
PrintOpcode(instr);
switch(instr->opcode)
{
case STR_OP:
case MCPY_OP:
Add(instr->u.base.src1);
Add(instr->u.base.src2);
break;
case LDC_OP:
Add(instr->u.ldc.dst);
break;
case BTRUE_OP:
case BFALSE_OP:
Add(instr->u.bj.src);
break;
case CALL_OP:
cout << "CALL OP" <<endl;
break;
case MBR_OP:
Add(instr->u.mbr.src);
break;
case RET_OP:
if (instr->u.base.src1 != NO_REGISTER)
Add(instr->u.base.src1);
break;
case CVT_OP:
case CPY_OP:
case NEG_OP:
case NOT_OP:
case LOAD_OP:
Add(instr->u.base.dst);
Add(instr->u.base.src1);
break;
case LABEL_OP:
case JMP_OP:
break;
default:
Add(instr->u.base.dst);
Add(instr->u.base.src1);
Add(instr->u.base.src2);
break;
}
}
void Add(Variable var)
{
variableList.push_back(var);
}
void RemoveDuplicates()
{
if (variableList.size() > 0)
{
variableList.erase(unique(variableList.begin(), variableList.end()), variableList.end());
currentID = variableList.size();
}
}
VariableList()
{
currentID = 0;
}
VariableList(VariableList& varList, bool setLiveness = false, bool LiveVal = false)
{
currentID = 0;
for (int i = 0; i < varList.size(); i++)
{
Variable var(varList[i]);
if (setLiveness)
{
var.isLive = LiveVal;
}
variableList.push_back(var);
}
}
Variable& operator[] (int i)
{
return variableList[i];
}
int size()
{
return variableList.size();
}
vector<Variable>::iterator begin()
{
return variableList.begin();
}
vector<Variable>::iterator end()
{
return variableList.end();
}
protected:
int currentID;
vector<Variable> variableList;
void Add(simple_reg* reg, bool checkForDuplicates = false)
{ cout << "Register Check" <<endl;
if (reg == null)
{
cout << "null detected" << endl;
return;
}
if (reg->kind == PSEUDO_REG)
{
if (!checkForDuplicates || (checkForDuplicates && find(variableList.begin(), variableList.end(), reg->num) != variableList.end()))
{
cout << "Adding... Reg " << reg->num << endl;
Variable var(reg->num, currentID);
variableList.push_back(var);
currentID++;
}
}
}
};
When I do this though, every instruction goes to the default case statement, even though I knwo for a fact some instructions shouldn't. If I change GenerateVariableList to
void GenerateVariableList()
{
for (int i = 0; i < allInstrs.size(); i++)
{
PrintOpcode(allInstrs[i]);
Variables.Add(allInstrs[i]);
}
Variables.RemoveDuplicates();
}
so that there is now a second PrintOpCode in addition to the one in Variables.Add, the program behaves correctly. I can't understand why adding a second PrintOpcode makes it work correctly. All print Opcode is is a function with a switch statement that just prints out a specific string depending on what the value of one of simple_instr's fields is.
VariableList Variables is contained inside of a separate struct called CFG
If you need more information/code i can provide it. If the answer is obvious I apologize, I don't program in C++ very often
EDIT:
One of the answers left, deleted now though, got me the fix.
Previously I was doing
static vector<Instruction*> ConvertLinkedListToVector(simple_instr* instructionList)
{
vector<Instruction*> convertedInstructions;
int count = 0;
for (simple_instr* current = instructionList; current; count++, current = current->next)
{
//Instruction* inst = new Instruction(*current);
Instruction inst = Instruction(*current);
inst.Id = count;
convertedInstructions.push_back(&inst);
}
return convertedInstructions;
}
to make the vector, but after reading that answer I changed it back to using "new" and it works correctly now. Thanks for the help, sorry for the dumb question heh
Most likely the const simple_instr& simple passed to your constructor goes out of scope, and you keep an invalid reference/pointer to a simple_instr.
Possibly not related your problem, but certainly a potential source of strange behaviour: Your Instruction(const simple_instr& simple) constructor may be getting called when you don't intend it. Mark it explicit...
explicit Instruction(const simple_instr& simple) ...
If that causes compiler errors, then that's progress :-) You might need to write a copy constructor to make them go away, and explicitly call the old constructor where you need to.
So, there are several suspicious observations:
In your definition of VariableList you use a type called Variable - how is that type defined?
Iterating over a container should be done using an iterator:
for (vector<Intruction *>::iterator it = allInstrs.begin();
it != allInstrs.end();
++it) {
Variables.Add(*it);
}
You should consider using a vector of boost::shared_ptr, or a boost::ptr_vector instead of a vector of pointers.
I can give you a huge general overview of "don'ts" relating to your code.
You are right in this case to use classes "deriving" from simple_instr but you are doing it wrong, given that later on you do a switch statement based on type. A switch-statement based on type (rather than state) is an anti-pattern. You should be calling some virtual method of your base class.
You almost certainly do not want your derived class to copy from the base class. You want to construct it with the parameters to construct its base-class.
You want a vector of the base class pointers? And to manage lifetime probably shared_ptr
const-correctness. Some of your methods like size() should certainly be const. For others you might want two overloads.
i have a problem with my program. It should be program that recognize palindome through the stack. Everything works great, only thing that don't work is printing stacks(original and reversed) after the funcion is done.
Here is my entire code, and the problem is at case d and e:
#include <iostream>
using namespace std;
const int MAXSTACK = 21;
class stack {
private:
int stop;
char stk[MAXSTACK];
public:
stack();
~stack();
stack(const stack& s);
void push(const char c);
char pop();
char top(void);
int emptystack(void);
int fullstack(void);
void stack_print(void);
int stack::create(void);
};
stack::stack()
{
stop = 0;
}
stack::~stack() { }
stack::stack(const stack& s)
{
stop = s.stop;
strcpy(stk,s.stk);
}
void stack::push(const char c)
{
stk[stop++] = c;
}
char stack::pop()
{
return stop--;
}
char stack::top(void)
{
return stk[stop - 1];
}
int stack::emptystack(void)
{
return !stop;
}
int stack::fullstack(void)
{
return stop == MAXSTACK;
}
void stack::stack_print(void)
{
for (int i=0; i<stop; i++)
cout<<stk[i];
cout<<endl;
}
int stack::create(void)
{
return !stop;
}
char menu()
{
char volba;
cout<<"\n";
cout<<" **********.\n";
cout<<"\n";
cout<<" a ... make new containers\n";
cout<<" b ... delete content\n";
cout<<" c ... enter string\n";
cout<<" d ... print on screen first stack\n";
cout<<" e ... print on screen first stack\n";
cout<<" f ... is it palindrom\n";
cout<<" x ... exit\n";
cout<<"\n your choice : ";
cin >> volba;
return volba;
}
int main() {
char palindrome[MAXSTACK];
char volba;
stack original,reversed;
int stackitems = 0,i;
//cin.getline(palindrome,MAXSTACK);
do{
volba = menu();
switch (volba)
{
case'a':
{
original.create();
reversed.create();
cout<<"done'";
break;
}
case'b':
{
original.emptystack();
reversed.emptystack();
cout<<"empty";
break;
}
case'c':
{
cout<<"enter your string"<<endl;
cin.get();
//cin.get();
cin.getline(palindrome,MAXSTACK);
for(int o = 0; o < strlen(palindrome); o++)
if (isalpha(palindrome[o]))
{
original.push(tolower(palindrome[o]));
stackitems++;
}
original.stack_print();
break;
}
case'd':
{
original.~stack();
for(int g = 0; g < strlen(palindrome); g++)
original.push(tolower(palindrome[g]));
original.stack_print();
}
/*//cin.getline(palindrome,MAXSTACK);
for(int g = 0; g < strlen(palindrome); g++)
if (isalpha(palindrome[g]))
{
original.push(tolower(palindrome[g]));
stackitems++;
}
}
original.stack_print();*/
break;
/*{
cout<<"original: ";
original.stack_print();
break;
}*/
break;
case'e':
{
cout<<"reversed:"<<endl;
for( i = 0; i < stackitems; i++) {
reversed.push(original.top());
original.pop();
}
reversed.stack_print();
}
break;
case'f':
{
for( i = 0; i < stackitems / 2; i++) {
reversed.push(original.top());
original.pop();
}
if (stackitems % 2)
original.pop();
while (!original.emptystack()) {
if (original.top() != reversed.top()) break;
original.pop(); reversed.pop();
}
if (original.emptystack())
cout << "it is palindrom\n";
else
cout << "not palindrom\n";
break;
}
default:cout<<"!??!";
}
} while(volba!='x');
}
You've explicitly called your stack's destructor. There is almost never a good reason to do this. If the stack is a local ("on the stack", hee hee), the compile will do it for you. If it's on the heap, created with new, call delete on it, which will cause the compiler to call the destructor.
case'd':
{
original.~stack();
You have commented palindrome reading :)
//cin.getline(palindrome,MAXSTACK);
There are a few things I would like to respond with. First, I think GMan, tpdi, and Vinay all have good points. This FAQ explains why calling the destructor on a local variable is a bad idea.
I realize this is just a simple homework problem and you are probably just trying to keep your stack class lightweight, but you might consider using a container class instead of an array of characters in your stack class.
Next, I'm not sure your emptystack and create functions are doing what you think they are doing. When you declare your original and reversed stack classes in the main program the memory is allocated for your internal character array. It's not really necessary in this case to have a create function. Perhaps if you were allocating memory on the heap for your character array, you would put that code into the create function (if you chose to leave it out of the constructor for some reason), but that's not the case here.
Similarly, emptystack isn't really doing anything. It would be better to have empty stack set the stop member variable to 0. At least that way the stack would appear to be empty the next time someone tried to use it.
There's a lot more that could be said about this class, but it might be better if you tried some of the suggestions here like using the std::stack and debugging. This is, after all, your homework assignment: it will help you a lot more in the future if you find the solution yourself!