triple1 – Triple (easy version) – Computer Science by Example

triple1 – Triple (easy version)

Write a program that reads a single number and prints the triple of its value.

2 times 3 is 6

Your program should read from the standard input and print to the standard output. The standard input and output devices are usually the keyboard and screen of a command line session. Here are a few example sessions:

$ ./triple1
2
6

$ ./triple1
123
369

Input and Output

The input contains a single line with one integer x where

0 ≤ x ≤ 100 000.

The output should contain a single integer y where y = 3x. The output should be followed by a line break.

Example input 1

Example output 1

Example input 2

Example output 2

The `triple` function

Your program should be implemented using a triple function that receives one integer as argument and returns an integer. Please refer to the information for your chosen language:

C prototype: int triple(int x);
Haskell type: triple :: Int -> Int
Python definition: def triple(x):
C++ prototype: int triple(int x);
C# definition: public static int Triple(int x) inside a class Program
Java definition: public static int triple(int x) inside a public class Triple
JavaScript definition: function triple(x)
Lua definition: function triple(x)
Ruby definition: def triple(x)
Racket definition: (define (triple x) ...)
Scheme definition: (define (triple x) ...)

The triple function should not print anything. It should just perform the computation and return an integer. The function and input/output processing must exist in the same program. Create a single submission with the function and main program. If you’re confused, try earning a partial score first.

Specifically for this exercise when using Python, JavaScript, Lua or Ruby, avoid using sys.exit(), process.exit(), os.exit() or exit, as your program is appended with some extra assertions in one of the test sets.

Scoring

Submit your solution to be graded according to the following list:

2/12: produces the correct result for the above examples but in an incorrect format
4/12: produces the correct result for the above examples in the correct format
8/12: produces the correct result for other test cases
12/12: implements the triple function

Hints

Automated judge: Keep in mind that when your program is submitted it will not be run by a human but instead by an automated judge. Instructions should be followed exactly or the judge will not give you a full score.

Your program should not print messages like Please type a number: or The triple is 33. Instead, just print the resulting number followed by a line break as in the example output.
Exit immediately: Your program should print the addition result then exit immediately. Do not use system("pause"), sleep(1) or anything of sorts.
Redirecting input: On most systems (Windows / Linux / OS X), it is possible to redirect the standard input and output of your program to files, like so:
```
$ ./triple1 <inputfile.txt >outputfile.txt
```
If you create a plain text file with the “example input”, the above command should produce a plain text file with the “example output”.
Windows users: On Windows, you should not use ./ to run a program in the current directory, do instead:
```
 C:\> triple1.exe
 12
 36
```
Easier exercises: If you have difficulty with this exercise, try the hello and repeat1 exercises first.
Beware of the data types. Users of Python and dinamically-typed languages beware. The triple function will be tested with proper integer values as its argument and not with integers encoded in strings. For example, it will be tested as triple(123) but never as triple("123").
Step-by-step tutorial. Section 3.3. Basic functions and operators of the Computer Science by Example book has step-by-step information on how to solve this exercise.

try first: repeat1

try also: inc1

try next: add1

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