Data Reading and Formatting
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Data Reading and Formatting |
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Data Reading |
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Introduction |
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In previous lessons, we saw that the Console class allows using the Write() and the WriteLine() methods to display things on the screen. While the Console.Write() method is used to display something on the screen, the Console class provides the Read() method to get a value from the user. To use it, the name of a variable can be assigned to it. The syntax used is: |
VariableName = Console.Read(); This simply means that, when the user types something and presses Enter, what the user had typed would be given (the word is assigned) to the variable specified on the left side of the assignment operator. Read() doesn't always have to assign its value to a variable. For example, it can be used on its own line, which simply means that the user is expected to type something but the value typed by the user would not be used for any significant purpose. For example some versions of C# (even including Microsoft's C# and Borland C#Builder) would display the DOS window briefly and disappear. You can use the Read() function to wait for the user to press any key in order to close the DOS window. |
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Besides Read(), the Console class also provides the ReadLine() method. Like the WriteLine() member function, after performing its assignment, the ReadLine() method sends the caret to the next line. Otherwise, it plays the same role as the Read() function.
In most assignments of your programs, you will not know the value of a string when writing your application. For example, you may want the user to provide such a string. To request a string (or any of the variables we will see in this lesson), you can call the Console.Read() or the Console.ReadLine() function and assign it to the name of the variable whose value you want to retrieve. Here is an example: using System;
public class Exercise
{
public static void Main()
{
string FirstName;
Console.Write("Enter First Name: ");
FirstName = Console.ReadLine();
}
}
In C#, everything the user types is a string and the compiler would hardly analyze it without your explicit asking it to do so. Therefore, if you want to get a number from the user, first request a string. Here is an example: using System;
public class Exercise
{
public static void Main()
{
int Number;
string strNumber;
strNumber = Console.ReadLine();
}
}
After getting the string, you must convert it to a number. To perform this conversion, each data type of the .NET Framework provides a mechanism called Parse. To use Parse(), type the data type, followed by a period, followed by Parse, and followed by parentheses. In the parentheses of Parse, type the string that you requested from the user. Here is an example: using System;
public class Exercise
{
public static void Main()
{
int Number;
string strNumber;
strNumber = Console.ReadLine();
Number = int.Parse(strNumber);
}
}
An advanced but faster way to do this is to type Console.ReadLine() in the parentheses of Parse. This has the same effect. Here is an example: using System;
public class Exercise
{
public static int Main()
{
int Number;
Number = int.Parse(Console.ReadLine());
return 0;
}
}
As done with the regular numbers, you can request a date value from the user. This is also done by requesting a string from the user. Here is an example: using System;
namespace ValueRequests
{
class Exercise
{
static void Main()
{
string strDateHired;
strDateHired = Console.ReadLine();
}
}
}
After the user has entered the string you can then convert it to a DateTime value. Just like any value you request from the user, a date or time value that the user types must be valid, otherwise, the program would produce an error. Because dates and times follow some rules for their formats, you should strive to let the user know how you expect the value to be entered. By default, if you request only a date from the user and the user enters a valid date, the compiler would add the midnight value to the date. If you request only the time from the user and the user enters a valid time, the compiler would add the current date to the value. Later on, we will learn how to isolate either only the date or only the time.
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Instead of using two Write() or a combination of Write() and WriteLine() to display data, you can convert a value to a string and display it directly. To do this, you can provide two strings to the Write() or WriteLine() and separate them with a comma:
Here are examples: using System;
public class Exercise
{
public static void Main()
{
var FullName = "Anselme Bogos";
var Age = 15;
var HSalary = 22.74;
Console.WriteLine("Full Name: {0}", FullName);
Console.WriteLine("Age: {0}", Age);
Console.WriteLine("Distance: {0}", HSalary);
Console.WriteLine();
}
}
This would produce: Full Name: Anselme Bogos Age: 15 Distance: 22.74 As mentioned already, the numeric value typed in the curly brackets of the first part is an ordered number. If you want to display more than one value, provide each incremental value in its curly brackets. The syntax used is: Write("To Display {0} {1} {2} {n}", First, Second, Third, nth);
You can use the sections between a closing curly bracket and an opening curly bracket to create a meaningful sentence.
We mentioned earlier that everything the user types using the keyboard is primarily a string and it's your job to convert it to the appropriate type. In reverse, if you have a value that is not a string, you can easily convert it to a string. To support this, each .NET Framework data type provides a mechanism called ToString. Normally, in C#, as we mentioned with boxing, and as we have done so far, this conversion is automatically or transparently done by the compiler. In some cases, you will need to perform the conversion yourself. To convert a value of a primitive data type to a string, type the name of the variable, followed by a period, followed by ToString(). Here is an example: using System;
public class Exercise
{
public static void Main()
{
var FullName = "Anselme Bogos";
var Age = 15;
var HSalary = 22.74;
Console.WriteLine("Full Name: {0}", FullName);
Console.WriteLine("Age: {0}", Age.ToString());
Console.WriteLine("Distance: {0}", HSalary.ToString());
Console.WriteLine();
}
}
In some cases, you will type something in the parentheses of ToString().
To properly display data in a friendly and most familiar way, you can format it. Formatting tells the compiler what kind of data you are using and how you want the compiler to display it to the user. As it happens, you can display a natural number in a common value or, depending on the circumstance, you may prefer to show it as a hexadecimal value. When it comes to double-precision numbers, you may want to display a distance with three values on the right side of the decimal separator and in some cases, you may want to display a salary with only 2 decimal places. The System namespace provides a specific letter that you can use in the Write() or WriteLine()'s placeholder for each category of data to display. To format a value, in the placeholder of the variable or value, after the number, type a colon and one of the appropriate letters from the following table. If you are using ToString(), then, in the parentheses of ToString(), you can include a specific letter or combination inside of double-quotes. The letters and their meanings are:
Here are examples: using System;
public class Exercise
{
public static void Main()
{
var Distance = 248.38782;
var Age = 15;
var NewColor = 3478;
var HSalary = 22.74;
var HoursWorked = 35.5018473;
var WeeklySalary = HSalary * HoursWorked;
Console.WriteLine("Distance: {0}", Distance.ToString("E"));
Console.WriteLine("Age: {0}", Age.ToString());
Console.WriteLine("Color: {0}", NewColor.ToString("X"));
Console.WriteLine("Weekly Salary: {0} for {1} hours",
WeeklySalary.ToString("c"),
HoursWorked.ToString("F"));
Console.WriteLine();
}
}
This would produce: Distance: 2.483878E+002 Age: 15 Color: D96 Weekly Salary: $807.31 for 35.50 hours As you may have noticed, if you leave the parentheses of ToString() empty, the compiler would use a default formatting to display the value. As opposed to calling ToString(), you can use the above letters in the curly brackets of the first part of Write() or WriteLine(). In this case, after the number in the curly brackets, type the colon operator followed by the letter.
In the above programs, to display a line of text, we easily used Write() or WriteLine(). To position text of different lengths one above the other, we had to "corrupt" a string by including extra-empty spaces. Such a technique is uncertain and less professional. Fortunately, you can highly format how a string or a line of text should display. The .NET Framework provides mechanisms to control the amount of space used to display a string of text and how to align that string on its line. To specify the amount of space used to display a string, you can use its placeholder in Write() or WriteLine(). To do this, in the placeholder, type the 0 or the incrementing number of the placer and its formatting character if necessary and if any. Then, type a comma followed by the number of characters equivalent to the desired width. Here are examples: using System;
public class Exercise
{
public static void Main()
{
var FullName = "Anselme Bogos";
var Age = 15;
var HSalary = 22.74;
Console.WriteLine("Full Name: {0,20}", FullName);
Console.WriteLine("Age:{0,14}", Age.ToString());
Console.WriteLine("Distance: {0:C,8}", HSalary.ToString());
Console.WriteLine();
}
}
This would produce: Full Name: Anselme Bogos Age: 15 Distance: 22.74 The sign you provide for the width is very important. If it is positive, the line of text is aligned to the right. This should be your preferred alignment for numeric values. If the number is negative, then the text is aligned to the left.
As mentioned earlier, when the user enters a date value for a DateTime variable, the compiler adds a time part to the value. Fortunately, if you want to consider only the date or only the time part, you can specify this to the compiler. To support this, the DateTime data type provides a series of letters you can use to format how its value should be displayed to the user. The character is entered in the placeholder of the DateTime variable after the 0 or the incremental numeric value.
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Practical
Learning: Introducing Data Reading