Unit 1: Introduction to C# PRACTICAL UNDERSTANDING Flashcards
1
Q
SYNTAX AT THE BEGINNING OF THE PROGRAM
A
using System;
namespace HelloWorld
{
class Program
{
static void Main(string[] args)
{
2
Q
using System
A
means that we can use classes from the System namespace.
3
Q
A blank line.
A
C# ignores white space. However, multiple lines makes the code more readable.
4
Q
namespace
A
is used to organize your code, and it is a container for classes and other namespaces.
5
Q
The curly braces {}
A
marks the beginning and the end of a block of code.
6
Q
class is a
A
container for data and methods, which brings functionality to your program.
Every line of code that runs in C# must be inside a class. In our example, we named the class Program.
7
Q
Another thing that always appear in a C# program, is the Main method.
A
Any code inside its curly brackets {} will be executed.
You don’t have to understand the keywords before and after Main. You will get to know them bit by bit while reading this tutorial.
8
Q
If you omit the using System line
A
you would have to write System.Console.WriteLine() to print/output text.
9
Q
Console is a class of the
A
System namespace,
10
Q
Every C# statement ends with a
A
semicolon ;
11
Q
“MyClass” and “myclass” has different meaning. BECAUSE
A
C# is case-sensitive:
12
Q
Single-line comments start with
A
two forward slashes//
13
Q
Multi-line comments start with
A
/*
14
Q
Multi-line ends with
A
*/
15
Q
To output values or print text in C#, you can use the
A
WriteLine() method
16
Q
This will output Hello World….?
A
Console.WriteLine(“Hello World!”);
17
Q
Console.WriteLine(9 + 3);
A
This will output 12
18
Q
There is also a method, which is similar to WriteLine().
A
Write()
19
Q
The only difference is that it does not insert a new line at the end of the output
A
Write()
IT PRINTS ON THE SAME LINE
20
Q
stores integers (whole numbers), without decimals, such as 123 or -123
A
int
21
Q
stores floating point numbers, with decimals, such as 19.99 or -19.99
A
double -
22
Q
stores single characters, such as ‘a’ or ‘B’. Char values are surrounded by single quotes
A
char
23
Q
- stores text, such as “Hello World”. String values are surrounded by double quotes
A
string
24
Q
- stores values with two states: true or false
A
bool
25
To create a variable, you must specify the type and assign it a value:
WHAT IS THE SYNTAX
type variableName = value;
26
type variableName = value;
Where type is a C# type (such as int or string), and variableName is the name of the variable (such as x or name). The equal sign is used to assign values to the variable.
27
Create a variable called name of type string and assign it the value "John":
string name = "John";
Console.WriteLine(name);
28
Create a variable called myNum of type int and assign it the value 15:
int myNum = 15;
Console.WriteLine(myNum);
29
You can also declare a variable without assigning the value, and assign the value later:
int myNum;
myNum = 15;
Console.WriteLine(myNum);
30
int myNum = 15;
myNum = 20; // myNum is now 20
Console.WriteLine(myNum);
if you assign a new value to an existing variable, it will overwrite the previous value:
31
A demonstration of how to declare variables of other types:
int myNum = 5;
double myDoubleNum = 5.99D;
char myLetter = 'D';
bool myBool = true;
string myText = "Hello";
32
If you don't want others (or yourself) to overwrite existing values...
you can add the const keyword in front of the variable type.
33
If you don't want others (or yourself) to overwrite existing values...
const int myNum = 15;
myNum = 20; // error
34
string name = "John";
Console.WriteLine("Hello " + name);
To combine both text and a variable, use the + character:
35
string firstName = "John ";
string lastName = "Doe";
string fullName = firstName + lastName;
Console.WriteLine(fullName);
You can also use the + character to add a variable to another variable:
36
int x = 5;
int y = 6;
Console.WriteLine(x + y); // Print the value of x + y
For numeric values, the + character works as a mathematical operator (notice that we use int (integer) variables here):
37
int x = 5;
int y = 6;
Console.WriteLine(x + y); // Print the value of x + y
x stores the value 5
y stores the value 6
Then we use the WriteLine() method to display the value of x + y, which is 11
38
int x = 5, y = 6, z = 50;
Console.WriteLine(x + y + z);
To declare more than one variable of the same type, use a comma-separated list:
39
int x, y, z;
x = y = z = 50;
Console.WriteLine(x + y + z);
You can also assign the same value to multiple variables in one line:
40
The general rules for naming variables are:
Names can contain letters, digits and the underscore character (_)
Names must begin with a letter
Names should start with a
lowercase letter and it cannot contain whitespace
Names are case sensitive ("myVar" and "myvar" are different variables)
Reserved words (like C# keywords, such as int or double) cannot be used as names
41
Implicit Casting
Implicit casting is done automatically when passing a smaller size type to a larger size type:
42
int myInt = 9;
double myDouble = myInt; // Automatic casting: int to double
Console.WriteLine(myInt); // Outputs 9
Console.WriteLine(myDouble); // Outputs 9
Implicit casting is done automatically when passing a smaller size type to a larger size type:
43
Explicit Casting
Explicit casting must be done manually by placing the type in parentheses in front of the value:
double myDouble = 9.78;
int myInt = (int) myDouble; // Manual casting: double to int
Console.WriteLine(myDouble); // Outputs 9.78
Console.WriteLine(myInt); // Outputs 9
44
Type Conversion Methods
?
It is also possible to convert data types explicitly by using built-in methods, such as Convert.ToBoolean, Convert.ToDouble, Convert.ToString, Convert.ToInt32 (int) and Convert.ToInt64 (long):
44
Type Conversion Methods
?
It is also possible to convert data types explicitly by using built-in methods, such as Convert.ToBoolean, Convert.ToDouble, Convert.ToString, Convert.ToInt32 (int) and Convert.ToInt64 (long):
45
It is also possible to convert data types explicitly by using built-in methods, such as Convert.ToBoolean, Convert.ToDouble, Convert.ToString, Convert.ToInt32 (int) and Convert.ToInt64 (long):
int myInt = 10;
double myDouble = 5.25;
bool myBool = true;
Console.WriteLine(Convert.ToString(myInt)); // convert int to string
Console.WriteLine(Convert.ToDouble(myInt)); // convert int to double
Console.WriteLine(Convert.ToInt32(myDouble)); // convert double to int
Console.WriteLine(Convert.ToString(myBool)); // convert bool to string
46
// Type your username and press enter
Console.WriteLine("Enter username:");
47
The Console.ReadLine() method returns a string. Therefore, you cannot get information from another data type, such as int. The following program will cause an error:
Console.WriteLine("Enter your age:");
int age = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("Your age is: " + age);
48
+ Addition
Adds together two values x + y
49
- Subtraction
Subtracts one value from another x - y
50
* Multiplication
Multiplies two values x * y
51
/ Division
Divides one value by another x / y
52
% Modulus
Returns the division remainder x % y
53
++ Increment
increase a value by 1
54
++ Increment
Increases the value of a variable by 1 x++
55
-- Decrement
Decreases the value of a variable by 1 x--
56
x = 5 is the same thing as?
x = 5
57
x += 3 is the same thing as?
x = x + 3
58
x -= 3
x = x - 3
59
x *= 3
x = x * 3
60
x /= 3
x = x / 3
61
x %= 3
x = x % 3
62
x &= 3
x = x & 3
63
x |= 3
x = x | 3
64
x ^= 3
x = x ^ 3
65
x >>= 3
x = x >> 3
66
x <<= 3
x = x << 3
67
x == y
== Equal to
68
!= x != y
Not equal
69
> x > y
Greater than
70
< x < y
Less than
71
>= x >= y
Greater than or equal to
72
<= x <= y
Less than or equal to
73
&& Logical and
Returns True if both statements are true
74
|| Logical or
Returns True if one of the statements is true
75
! Logical not
Reverse the result, returns False if the result is true
76
IF STATEMENT EXAMPLE
if (20 > 18)
{
Console.WriteLine("20 is greater than 18");
}
77
IF... ELSE STATEMENT
int time = 20;
if (time < 18)
{
Console.WriteLine("Good day.");
}
else
{
Console.WriteLine("Good evening.");
}
// Outputs "Good evening."
78
Short Hand If...Else (Ternary Operator)
variable = (condition) ? expressionTrue : expressionFalse;
79
C# Switch Statements EXAMPLE
int day = 4;
switch (day)
{
case 1:
Console.WriteLine("Monday");
break;
case 2:
Console.WriteLine("Tuesday");
break;
case 3:
Console.WriteLine("Wednesday");
break;
case 4:
Console.WriteLine("Thursday");
break;
case 5:
Console.WriteLine("Friday");
break;
case 6:
Console.WriteLine("Saturday");
break;
case 7:
Console.WriteLine("Sunday");
break;
}
// Outputs "Thursday" (day 4)
80
wHILE LOOP
int i = 0;
while (i < 5)
{
Console.WriteLine(i);
i++;
}
81
WHILE LOOP SYNTAX
while (condition)
{
// code block to be executed
}
82
C# For Loop
for (statement 1; statement 2; statement 3)
{
// code block to be executed
}
83
C# Break
The break statement can also be used to jump out of a loop.
for (int i = 0; i < 10; i++)
{
if (i == 4)
{
break;
}
Console.WriteLine(i);
}
84
C# Continue
for (int i = 0; i < 10; i++)
{
if (i == 4)
{
continue;
}
Console.WriteLine(i);
}
85
METHOD??
A method is a block of code which only runs when it is called.
86
METHOD ARE FUNCTIONS?
Methods are used to perform certain actions, and they are also known as functions.
87
A method is defined with the name of the method, followed by parentheses ()
class Program
{
static void MyMethod()
{
// code to be executed
}
}
88
IF THE CLASS IS FRUIT
89
HER
