Question

Using C++

1. What is type casting (page 103) and why is it used incorrectly in the following code?

int books = 30;
int months = 4;
double perMonth;
perMonth = static_cast<double> (books/months);
cout << perMonth << endl;

Answer 1

Type Casting: It is a way to change the data type explicitly by a user.

Why it is USed??

Some times we assume the data type of some particular type, but in between, we might need to switch a different type so as to be more precise or the new type is more valid.

In this example:

We start with books which is an integer

months which is also an integer.

Now perMonth is defined as double which is the ratio of books and months.

This only makes sense that perMonth is double so it is defined double.

Expected Answer = 7.5

Actual Answer when we run the code will be 7 because we are dividing two integers.

In c++ when two integers are divided the output is always an integer value.

SO What is wrong in this declaration!

There is casting applied after the division has taken place instead it should be done before the division.

SO the correct code is as follows

Make books as double LIKE THIS

#include <iostream>
using namespace std;

int main() {
   // your code goes here
   int books = 30;
   int months = 4;
   double perMonth;
   perMonth = static_cast<double> (books) / (months);
   cout << perMonth << endl;
   return 0;
}

OR Make months as double LIKE THIS

#include <iostream>
using namespace std;

int main() {
   // your code goes here
   int books = 30;
   int months = 4;
   double perMonth;
   perMonth = (books) / static_cast<double> (months);
   cout << perMonth << endl;
   return 0;
}

OR Make months and books both as double LIKE THIS

#include <iostream>
using namespace std;

int main() {
   // your code goes here
   int books = 30;
   int months = 4;
   double perMonth;
   perMonth = static_cast<double> (books) / static_cast<double> (months);
   cout << perMonth << endl;
   return 0;
}

All the three above codes are perfectly fine and will give 7.5 as a result.

Please comment for any further assistance.