abnormal behaviour while displaying char array in C++ after object initialization - c++

Question

main():
char inp[] = "(A+B)/(C*D))";
Infix i;
cout << "In main: " << inp /* + ')' */ << endl << endl;
Here is Infix constructor:
Infix() {
push('(');
cout << "Element In Stack: " << *returnElement(returnTop()) << endl;
outputString = "";
strcpy(operatorArray, "/*-+%");
cout << "Operator Array: " << operatorArray << endl;
}
Infix is inheriting from a class 'Stack':
class Stack{
int top = -1;
char arr[100];
public:
bool push(char);
char pop();
char peek();
bool isEmpty();
void displayAll();
char returnTop() { return top;}
char* returnElement(int i) {
if(i > 98){
cout << "StackOutOfIndex";
return nullptr;
}
return &arr[i];
}
};
When I run the code in main, it displays unusual output:
Element In Stack: (
Operator Array: /*-+%
In main: +%
Stack Object Destroyed!
But, when in main, if the comment the line declaring 'Infix' object declaration, the code runs fine:
In main: (A+B)/(C*D))
EDITS:
Stack Class
#include<iostream>
using namespace std;
class Stack{
int top = -1;
char arr[100];
public:
bool push(char);
char pop();
char peek();
bool isEmpty();
void displayAll();
char returnTop() { return top;}
char* returnElement(int i) {
if(i > 98){
cout << "StackOutOfIndex";
return nullptr;
}
return &arr[i];
}
};
bool Stack:: push(char elementToPush) {
if(top > 98) {
cout << "\nStack Overflow!!";
return false;
} else {
arr[++top] = elementToPush;
return true;
}
}
char Stack:: pop() {
if(top <= -1) {
cout << "\nStack Underflow!!";
return ' ';
} else {
return (arr[top--]);
}
}
char Stack:: peek() {
if(top > 98) {
cout << "\nStack Overflow!!";
return ' ';
} else {
return arr[top];
}
}
bool Stack:: isEmpty() {
return (top <= 0);
}
void Stack:: displayAll() {
if(top <= -1) {
cout << "null";
return;
}
int i = top;
while (i >= 0) {
cout << arr[i] << " ";
--i;
}
cout << "\n";
}
Infix Class
#include<iostream>
#include<cstring>
#include<D:\Programs\11Stack.cpp>
using namespace std;
class Infix : public Stack {
string outputString;
char operatorArray[];
public:
Infix() {
push('(');
cout << "Element In Stack: " << *returnElement(returnTop()) << endl;
outputString = "";
strcpy(operatorArray, "/*-+%");
cout << "Operator Array: " << operatorArray << endl;
}
string infixToPostfix(char *, int);
bool manupulateOperator(char, int);
int checkPrecedence(char);
~Infix() {
cout << "\nStack Object Destroyed!" << endl;
}
};
string Infix:: infixToPostfix(char *str, int size) {
cout << "\nGiven String: " << str << endl;
int x;
for(int i = 0; i < size; ++size) {
x = str[i];
if(x != ' ') {
if(x == ')') {
while(returnTop() != '(') {
cout << pop() << " popped!\n";
}
cout << pop() << " popped!\n";
} else if(isalpha(x)) {
cout << x;
} /* else{ // scanned character is an operator
if(manupulateOperator(x, i)) {
} else {
return " ";
}
} */
}
}
return outputString;
}
bool Infix::manupulateOperator(char c, int position) {
try {
char topElement = *returnElement(returnTop());
if(checkPrecedence(c) == -1) {
cout << "\nErr\n";
}else if((checkPrecedence(c) > checkPrecedence(topElement)) || returnTop() == 0) {
push(c);
cout << c << " pushed!\n";
}
} catch(std::exception e) {
std::cerr << e.what() << '\n';
return false;
} catch (char* Ce) {
cout << Ce << endl;
}
return true;
}
int Infix::checkPrecedence(char c) {
/*
+ -> 1
- -> 1
* -> 2
/ -> 2
% -> 2
*/
switch(c) {
case '+':
return 1;
case '-':
return 1;
case '*':
return 2;
case '/':
return 2;
case '%':
return 2;
default:
// throw "Illegal Operator Detected!";
cout << "Illegal Operator Detected: " << c << endl;
return -1;
}
}
int main() {
cout << endl;
int x = 1;
char inp[] = "(A+B)/(C*D))";
//Infix i;
cout << "In main: " << inp /* + ')' */ << endl << endl;
// cout << i.infixToPostfix(input + ')', sizeof(input));
/* for(int i = 0; i < strlen(inp); ++i) {
cout << inp[i];
}
*/
return 0;
}

Answer 1

You are declaring operatorArray as an array of char but you are not assigning any memory for it! So, when you then call strcpy(operatorArray, "/*-+%"); in your Infix constructor, you are causing undefined behaviour by attempting to copy the given string constant to memory that hasn't been assigned - and this appears to be overwriting the inp[] array declared in your main.
To fix this, I would suggest giving your operatorArray member a specific size, which will be large enough to accommodate whatever string you want to copy to it - 8 characters will work in the sample code you've given:
class Infix : public Stack {
string outputString;
char operatorArray[8]; // Make this member a REAL array of characters.
//..

Answer 2

Your variable char operatorArray[] have no memory allocated when your constructor is called. When you use strcpy, you write to a place where you don't have permissions in your memory, and therefore on other informations.
To find these kinds of mistakes, I recommend using valgrind.

Answer 3

char operatorArray[]; is not allowed in Standard C++.
If you didn't see an error message then I would recommend adjusting compiler settings to follow the standard form of the language, this would have saved you a lot of time.