C++ Program to check whether the given expression is valid or not:

ExpressionValidation.cpp

#include<iostream>
#define maxi 1000

using namespace std;

template<class T>
class sstack{
    T a[maxi];
    int top;

    public:
        sstack();
        void push(T val);
        void pop();
        T peep();
        bool isempty();
        void display();
};

template<class T>
sstack<T>::sstack(){
    top=-1;
}

template<class T>
void sstack<T>::push(T val){
    if(top==maxi-1){
        cout<<"\nThe Stack is already full...";
    }
    a[++top]=val;
}

template<class T>
void sstack<T>::pop(){
    if(top!=-1)
        top--;
}

template<class T>
T sstack<T>::peep(){
    if(top!=-1)
        return a[top];
}

template<class T>
bool sstack<T>::isempty(){
    if(top==-1)return true;
    else return false;
}

template<class T>
void sstack<T>::display(){
    if(top!=-1){
        cout<<"\nThe Contents of the Stack is..";
        int x=top;
        while(x!=-1){
            cout<<a[x]<<" ";
            x--;
        }
    }
}

int main()
{
    sstack<char>s;
    string a;
    cout<<"Enter any expression..";
    cin>>a;
    int i;
    for(i=0;i<a.length();i++){
        if(s.isempty()){
            s.push(a[i]);
        }
        else if((s.peep()=='(' && a[i]==')')||(s.peep()=='{' && a[i]=='}')||(s.peep()=='[' && a[i]==']')||(s.peep()=='<' && a[i]=='>')){
            s.pop();
        }
        else{
            s.push(a[i]);
        }
    }
    if(s.isempty()){
        cout<<"The Expression is Valid.";
    }
    else{
        cout<<"The Expression is not Valid.";
    }
    return 0;
}