Why does my condition not work? - c++

Question

I have the following code:
#include <iostream>
using namespace std;
int a, b, sqr;
const int P = 3.14; //Later for circles...
string s1;
class MathsFunctions{
public:
virtual void square(int a, int b)=0;
};
class TriangleFunc: public MathsFunctions{
public:
void square(int a, int b){
sqr = (a * b)/2;
cout << "Square of triangle is: "<< sqr << endl;
}
};
class RectangleFunc: public MathsFunctions{
public:
void square(int a, int b){
sqr = a * b;
cout << "Square of rectangle is: "<< sqr << endl;
}
};
void getNumbers(){
cout << "Enter the first number: "<<endl;
cin >> a;
cout << "Enter the second number: "<< endl;
cin >> b;
}
void chooseTheFigure(){
cout << "Choose the figure (rectangle or triangle): "<< endl;
cin >> s1;
}
int main(){
chooseTheFigure();
getNumbers();
if(s1 == "rectangle" || "Rectangle"){
RectangleFunc r;
MathsFunctions * m = &r;
m -> square(a,b);
};
if (s1 == "triangle" || "Triangle"){
TriangleFunc t;
MathsFunctions *m = &t;
m -> square(a,b);
};
}
I created a program which is count the square of rectangle or triangle. There is a condition in main() but in the end program shows both results. How can I improve that?
Screenshot of output of the program:

Answer 1

This doesn't do what you think it does:
if(s1 == "rectangle" || "Rectangle"){
RectangleFunc r;
MathsFunctions * m = &r;
m -> square(a,b);
};
The if-expression above is evaluated as:
if((s1 == "rectangle") || ("Rectangle"))
// ^^^^^^^^^^^^^^^^^ or ^^^^^^^^^^
Now, the second part there, "Rectangle" is a string-literal which implicitly converts to a valid pointer. And any pointer other than nullptr or some zero like integer evaluates to true - always.
You probably meant to write:
if((s1 == "rectangle") || (s1 == "Rectangle")){
RectangleFunc r;
MathsFunctions * m = &r;
m -> square(a,b);
};
----------------------------------------
There are a few other nuances in your code, such
not having a vitual destructor in your base class and,
this:
const int P = 3.14; //Later for circles...
P will not hold the value you expect.

Answer 2

if(s1 == "rectangle" || "Rectangle"){
There are 2 conditions when this is true, the first is what you expect, the second is your bug because it's now what you meant to say in your code:
1) the input string s1, compared for equality to the string literal "rectangle" returns true, or
2) if the string-literal "Rectangle", by itself, is considered a true value.
As this conversion is essentially a "null pointer check", and the string literal is never null, this case is always true.
What you need is to repeat the test:
if(s1 == "rectangle" || s1 == "Rectangle"){

Answer 3

1.As WhiZtim pointed out, Or operator needs correction
if(s1 == "rectangle" || "Rectangle") {...}
will always be true as "Rectangle" is not null.
You should use string compare functions for strings (see strcmpi())
Edit
Regarding string functions, check this out:
Case-insensitive string comparison in C++