I declared an int variable with the value of the sum of another 3 int variables. when i print this variable, it shows a huge negative number

Question

#include <iostream>
#include <math.h>

using namespace std;

int main()
{
    int l,b,h;
    int s;
    s=(l+b+h);
    float ar=s*(s-l)*(s-b)*(s-h);
    float area;
    int ch;
    cout<<"How do you want to calculate the area?"<<endl;
    cout<<"1) simple formula"<<endl<<"2) heron's formula"<<endl;
    cin>>ch;
    if(ch==1){
        cout<<"Enter the sides of the triangle."<<endl;
        cin>>l>>b>>h;
        area=0.5*(b*h);
        cout<<"Area of the triangle is = "<<area<<endl;
    }
    else if (ch==2){
        cout<<"Enter the sides of the triangle."<<endl;
        cin>>l>>b>>h;
        cout<<s<<endl<<l+b+h<<endl;
        cout<<"The calculated area of the triangle is = "<<sqrt(ar)<<endl;
    }
    return 0;
}

It prints the correct value for l+b+h but, for s, it displays a huge negative number .I've tried changing the data type of s too. This happens in almost all my programs.

`l`, `b`, and `h` have unspecified values because you didn't initialize them. So the value of `s` is also unspecified. You cannot compute `s` until after you populate those values. — Cory Kramer, Sep 05 '17 at 16:55
In c++, when you assign an expression to a variable, you are actually assigning the immediate result of that expression. After `s=(l+b+h);` the variable `s` has the sum of whatever `l`, `b` and `h` had at that time. Changing any of those variables will not retroactively update `s`. — François Andrieux, Sep 05 '17 at 16:55
so...i'll have to type the s=(l+b+h) part after getting the inputs? — Manoj Vijayakumar, Sep 05 '17 at 16:56
@ManojVijayakumar Yes, and every time it's value should change. — François Andrieux, Sep 05 '17 at 16:57
Welcome to Stack Overflow! Sounds like you could use a [good C++ book](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) — NathanOliver, Sep 05 '17 at 16:58
@François Andrieux oh thanks a lot. it worked.@NathanOliver I'm new to the programming world and stackoverflow. — Manoj Vijayakumar, Sep 05 '17 at 16:58

score 0 · Answer 1 · answered Sep 05 '17 at 17:03

s is computed once (by reading uninitialized values, so UB).

You may create lambda instead:

auto s = [&](){ return l + b + h; };
auto ar = [&](){ return s() * (s() - l) * (s() - b) * (s() - h); };

and then

cout << "Enter the sides of the triangle." << endl;
cin >> l >> b >> h;
cout << s << endl << l + b + h << endl;
cout << "The calculated area of the triangle is = " << sqrt(ar) << endl;

Or simply compute the value after setting the values

cout << "Enter the sides of the triangle." << endl;
cin >> l >> b >> h;
const int s = l + b + h;
const int ar = s * (s - l) * (s - b) * (s - h);

cout << s << endl << l + b + h << endl;
cout << "The calculated area of the triangle is = " << sqrt(ar) << endl;

I declared an int variable with the value of the sum of another 3 int variables. when i print this variable, it shows a huge negative number

1 Answers1