Tutorial for Input and Output |
This post will try and introduce newcomers to the first and most basic thing they need to learn before submitting programs -- How to properly accept Input and print Output (I/O). I'll start off with a few guidelines and then conclude with an example from the CodeChef site.
For all the questions on our site, the input will be given to you from standard input (stdin for C users) and the result is expected on standard output (stdout for C users). This is the same as writing a program that accepts input from the keyboard and displays the results on the screen. I'm sure most of you have been programming that way already. However, a major difference is that you don't need to prompt the user for input, so stuff like:
"Please enter your name: "
are a big NO NO! You need to assume that the user entering the data at the other end knows what to enter and when to enter it. Similarly, while displaying the results, you need to display it in the exact format as is specified in the problem statement.
For figuring out the format in which data will be entered (given to you) and how you should display the results, you need to refer to the "Input" and “Output” section of the problem statement respectively. Please make sure that you are following the output specification to the decimal point. If you have one character out of place, your submission will be marked as incorrect
After reading the problem statement, you will be given a sample "Input” and the resulting expected “Output” your program should submit. Typically, you will be asked to run your program against multiple test cases. The number of test cases and the format of each test case will be clearly mentioned in the problem statement's "Input" section. More often than not, you will be required to display the result for each test case, so you will have as many results displayed as there are test cases.
Why so many test cases?
You must have studied about the different types of tests that you can run your program against in school. Some of them are:
- Boundary value testing
- Negative testing
- Stress testing
- and so on....
Now, each of these have a specific purpose, so the problem setter has kept many different types of tests to test the correctness and performance of your program for different types of inputs.
Let us move on to a specific example to see what is happening.
The problem we shall be tacking here is: Life, the Universe, and Everything
The problem statement:
Your program is to use the brute-force approach in order to find the Answer to Life, the Universe, and Everything. More precisely... rewrite small numbers from input to output. Stop processing input after reading in the number 42. All numbers at input are integers of one or two digits.
Input:
A list of integers separated by a new line.
Output:
All the integers before the integer '42'.
Sample Input:
1
2
88
42
99
Sample Output:
1
2
88
Here, the constraint on the input we have is that any input number n will be such that (0 <= n < 100).
The problem statement is pretty straightforward, but for this toy program, the problem setter may construct test cases where:
- The 1st number is 42
- The last number if 42
- There are 10000000 numbers before 42
The first 2 tests are boundary value tests, and the 3rd one is a performance test. Generally these problems have a time limit associated with them. You are required to solve the problem with the given constraints in the given time limit. This time limit is chosen such that a good solution in any language would be accepted.If you are stuck, the answers to this problem, in over 25 programming languages can be found at Sample Solutions
You can now go ahead and try out the problems in the easy set.
A few quick examples for Input/Output/IO in Python and a quick Ruby IO into as well.
