Stack Data Structure Parenthesis Matching - c++

Question

I was trying this parenthesis matching stack code and every time I run this it only gives me that parenthesis are not matching I don't know what is going wrong. Can you guys please help me out in this and tell me how can I improve this further and is this the right way to use stack in c++ because I was studying from a source that is using c language.
#include<iostream>
using namespace std;
struct stack
{
int size;
int top;
char *arr;
};
int isEmpty(struct stack *ptr)
{
if(ptr->top==-1)
{
return 1;
}
return 0;
}
int isFull(struct stack *ptr)
{
if (ptr->top == ptr->size-1)
{
return 1;
}
return 0;
}
void push(struct stack *ptr,char val)
{
if(isFull(ptr))
{
cout<<"stack overflow"<<endl;
}
else
{
ptr->top++;
ptr->arr[ptr->top] = val;
}
}
char pop(struct stack *ptr)
{
if (isEmpty(ptr))
{
cout<<"stack underflow"<<endl;
return -1;
}
else
{
char val = ptr->arr[ptr->top];
ptr->top-1;
return val;
}
}
int parenthesisMatch (char * exp)
{
struct stack * sp = new struct stack;
sp->size = 80;
sp->top = -1;
sp->arr = new char(sp->size);
for(int i=0; exp[i]!='\0'; i++)
{
if (exp[i] == '(')
{
push(sp,'(');
}
else if(exp[i] == ')')
{
if (isEmpty(sp))
{
return 0;
}
pop(sp);
}
}
if (isEmpty(sp))
{
return 1;
}
return 0;
}
int main()
{
char *exp = "((8)(*--$$9))";
if(parenthesisMatch(exp))
{
cout<<"The parenthesis is matching\n";
}
else
{
cout<<"The parenthesis is not matching\n";
}
return 0;
}

Answer 1

Just tried to debug the code and found 2 potential errors:
As correctly pointed out by #Welbog in the comments, to create an array, use sp->arr = new char[sp->size; in the function parenthesisMatch().
In the function pop(), the value of the top is not decremented correctly.
Have a look at the working code:
#include<iostream>
struct stack
{
int size;
int top;
char *arr;
};
int isEmpty(struct stack *ptr)
{
if(ptr->top==-1)
{
return 1;
}
return 0;
}
int isFull(struct stack *ptr)
{
if (ptr->top == ptr->size-1)
{
return 1;
}
return 0;
}
void push(struct stack *ptr,char val)
{
if(isFull(ptr))
{
std::cout<<"stack overflow"<<std::endl;
}
else
{
ptr->top++;
ptr->arr[ptr->top] = val;
}
}
char pop(struct stack *ptr)
{
if (isEmpty(ptr))
{
std::cout<<"stack underflow"<<std::endl;
return -1;
}
else
{
char val = ptr->arr[ptr->top];
ptr->top-=1;
return val;
}
}
int parenthesisMatch (char * exp)
{
struct stack * sp = new struct stack;
sp->size = 80;
sp->top = -1;
sp->arr = new char[sp->size];
for(int i=0; exp[i]!='\0'; i++)
{
if (exp[i] == '(')
{
push(sp,'(');
}
else if(exp[i] == ')')
{
if (isEmpty(sp))
{
return 0;
}
pop(sp);
}
}
if (isEmpty(sp))
{
return 1;
}
return 0;
}
int main()
{
char *exp = "((8)(*--$$9))";
if(parenthesisMatch(exp))
{
std::cout<<"The parenthesis is matching\n";
}
else
{
std::cout<<"The parenthesis is not matching\n";
}
return 0;
}