Console Input / Output
Reading and Writing to the Console
Imran Khan
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The Console Class
Provides methods for console input and output
Input
Read(…) – reads a single character
ReadKey(…) – reads a combination of keys
ReadLine(…) – reads a single line of characters
Output
Write(…) – prints the specified
argument on the console
WriteLine(…) – prints specified data to the
console and moves to the next line
4
Console.Write(…)
Printing an integer variable
int a = 15;
...
Console.Write(a); // 15
Printing more than one variable using a
formatting string
double a = 15.5;
int b = 14;
...
Console.Write("{0} + {1} = {2}", a, b, a + b);
// 15.5 + 14 = 29.5
Next print operation will start from the same line
5
Console.WriteLine(…)
Printing a string variable
string str = "Hello C#!";
...
Console.WriteLine(str);
Printing more than one variable using a
formatting string
string name = "Marry";
int year = 1987;
...
Console.Write("{0} was born in {1}.", name, year);
// Marry was born in 1987.
Next printing will start from the next line
6
Printing to the Console – Example
static void Main()
{
string name = "Peter";
int age = 18;
string town = "Sofia";
Console.Write("{0} is {1} years old from {2}.",
name, age, town);
// Result: Peter is 18 years old from Sofia.
Console.Write("This is on the same line!");
Console.WriteLine("Next sentence will be" +
" on a new line.");
Console.WriteLine("Bye, bye, {0} from {1}.",
name, town);
}
7
Printing a Menu – Example
double colaPrice = 1.20;
string cola = "Coca Cola";
double fantaPrice = 1.20;
string fanta = "Fanta Dizzy";
double zagorkaPrice = 1.50;
string zagorka = "Zagorka";
Console.WriteLine("Menu:");
Console.WriteLine("1. {0} – {1}",
cola, colaPrice);
Console.WriteLine("2. {0} – {1}",
fanta, fantaPrice);
Console.WriteLine("3. {0} – {1}",
zagorka, zagorkaPrice);
Console.WriteLine("Have a nice day!");
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Reading from the Console
We use the console to read information from
the command line
We can read:
Characters
Strings
Numeral types (after conversion)
To read from the console we use the methods
Console.Read() and Console.ReadLine()
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Console.Read()
Gets a single character from the console (after
[Enter] is pressed)
Returns a result of type int
Returns -1 if there aren’t more symbols
To get the actually read character we
need to cast it to char
int i = Console.Read();
char ch = (char) i; // Cast the int to char
// Gets the code of the entered symbol
Console.WriteLine("The code of '{0}' is {1}.", ch, i);
10
Waits Console.ReadKey()
until a
combi
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ConsoleKeyInfo key = Console.ReadKey();
singl
Console.WriteLine();
Console.WriteLine("Character entered: " + key.KeyChar);
e
Console.WriteLine("Special keys: " + key.Modifiers);
char
acter 11
Console.ReadLine()
Gets a line of characters
Returns a string value
Returns null if the end of the input is reached
Console.Write("Please enter your first name: ");
string firstName = Console.ReadLine();
Console.Write("Please enter your last name: ");
string lastName = Console.ReadLine();
Console.WriteLine("Hello, {0} {1}!",
firstName, lastName);
12
Reading Numeral Types
Numeral types can not be read directly from the
console
To read a numeral type do the following:
1. Read a string value
2. Convert (parse) it to the required numeral type
int.Parse(string) – parses a string to int
string str = Console.ReadLine()
int number = int.Parse(str);
Console.WriteLine("You entered: {0}", number);
13
Converting Strings to Numbers
Numeral types have a method Parse(…) for
extracting the numeral value from a string
int.Parse(string) – string int
long.Parse(string) – string long
float.Parse(string) – string float
Causes FormatException in case of error
string s = "123";
int i = int.Parse(s); // i = 123
long l = long.Parse(s); // l = 123L
string invalid = "xxx1845";
int value = int.Parse(invalid); // FormatException
14
Reading Numbers from the
Console – Example
static void Main()
{
int a = int.Parse(Console.ReadLine());
int b = int.Parse(Console.ReadLine());
Console.WriteLine("{0} + {1} = {2}",
a, b, a+b);
Console.WriteLine("{0} * {1} = {2}",
a, b, a*b);
float f = float.Parse(Console.ReadLine());
Console.WriteLine("{0} * {1} / {2} = {3}",
a, b, f, a*b/f);
}
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Converting Strings to
Numbers (2)
Converting can also be done using the methods of
the Convert class
Convert.ToInt32(string) – string int
Convert.ToSingle(string)– string float
Convert.ToInt64(string)– string long
Internally uses the parse methods of the numeral
types
string s = "123";
int i = Convert.ToInt32(s); // i = 123
long l = Convert.ToInt64(s); // l = 123L
string invalid = "xxx1845";
int value = Convert.ToInt32(invalid); // FormatException
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Error Handling when Parsing
Sometimes we want to handle the errors when
parsing a number
Two options: use try-catch block or TryParse()
Parsing with TryParse():
string str = Console.ReadLine();
int number;
if (int.TryParse(str, out number))
{
Console.WriteLine("Valid number: {0}", number);
}
else
{
Console.WriteLine("Invalid number: {0}", str);
}
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Printing a Letter – Example
Console.Write("Enter person name: ");
string person = Console.ReadLine();
Console.Write("Enter company name: ");
string company = Console.ReadLine();
Console.WriteLine(" Dear {0},", person);
Console.WriteLine("We are pleased to tell you " +
"that {1} has chosen you to take part " +
"in the \"Introduction To Programming\" " +
"course. {1} wishes you good luck!",
person, company);
Console.WriteLine(" Yours,");
Console.WriteLine(" {0}", company);
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Calculating Area – Example
Console.WriteLine("This program calculates " +
"the area of a rectangle or a triangle");
Console.Write("Enter a and b (for rectangle) " +
" or a and h (for triangle): ");
int a = int.Parse(Console.ReadLine());
int b = int.Parse(Console.ReadLine());
Console.Write("Enter 1 for a rectangle or 2 " +
"for a triangle: ");
int choice = int.Parse(Console.ReadLine());
double area = (double) (a*b) / choice;
Console.WriteLine("The area of your figure " +
" is {0}", area);
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We Summary
have
discus
sed
the
basic
input
and
outpu
t
meth
ods of
the 20
1. Write Exercises
a
progra
m that
reads
3
intege
r
numb
ers
from
the
consol
e and
prints 21
4. Write Exercises (2)
a
progra
m that
reads
two
positiv
e
intege
r
numb
ers
and
prints
how 22
7. Write Exercises (3)
a
progr
am
that
gets
a
numb
er n
and
after
that
gets
more
n 23
