1.4.1. Exercises: Input and Output

1.4.1. Exercises: Input and Output
	1.4. Input and Output

[ fromfile: cppintro.xml id: x-inputoutput ]

Using Example 1.2, do the following experiments:
- First, compile and run it, to see its normal behavior.
- What happens if you enter a non-numeric value for the birth year?
- What happens if you enter a name like Curious George as your name?
- What happens if you remove the following line?
```
using namespace std; 
```
- Replace the statement
```
 cin >> yourName; 
```
  with the statement
```
 getline(cin, yourName); 
```
  and try Curious George again.
- Can you explain the differences in behavior between cin >> and getline()? We discuss this in Section 1.7.
- Add some more questions to the program that require a variety of numerical and string answers and test the results.

Example 1.3. src/early-examples/fac2.cpp


#include <iostream> 

long factorial(long n) {
    long ans = 1;
    for (long i = 2; i <= n; ++i) {
        ans = ans * i;
        if (ans < 0) {
            return -1;
        }
    }
    return ans;
}

int main() {
    using namespace std;
    cout << "Please enter n: " << flush;
    long n;        
    cin >> n;       

    if (n >= 0) { 
        long nfact = factorial(n);
        if (nfact < 0) {
            cerr << "overflow error: " 
                 << n << " is too big." << endl;
        }
        else {
            cout << "factorial(" << n << ") = "
                 << nfact << endl;
        }
    }
    else {
        cerr << "Undefined:  "
             << "factorial of a negative number: " << n << endl;
    }
    return 0;
}

	long int
	read from stdin, try to convert to long

Test Example 1.3 with a variety of input values, including some non-numeric values.
Determine the largest input value that will produce a valid output.
Can you change the program so that it will produce valid results for larger input values?
Modify the program so that it cannot produce invalid results.
Explore the effects of using the statement
```
 if (cin >> n)   {  ...  } 
```
to enclose the processing of n in this program. In particular, try entering non-numeric data after the prompt. This is an example of the use of a conversion operator, which we discuss in more detail in Section 2.13.
Modify the program so that it will accept values from the user until the value 9999 is entered.

In the dist directory we have provided a tarball named src.tar.gz which contains all of the code examples in this book. An extremely valuable practice that you should adopt is to take each code example, build and run it to see how it is supposed to behave, and then break it by making various changes to see what happens. Sometimes you will learn how the compiler will respond to a particular syntax error that your change produced. The compiler can be your best friend if you can learn to understand its language. Other times you can see how the runtime behavior of the program is affected by a particular logic error that you produced. In each case, the experience will strengthen your understanding of C++ programming.


1.4. Input and Output		1.5. qmake, Project Files, and Makefile