3.5. Lab 03
Use a Word file to paste your screenshots.
Add notes to make your submission clear.
Number the questions clearly (e.g., 3.5.1. Return Statement).
Unclear screenshots will result in grade penalty.
3.5.1. Return Statement
Perform the following for this part of the lab:
Copy this code into a project called Returns.
Run the code.
Study the code and make sure you understand how every line of the code works.
Write brief comments (after //) at the right of each line to explain what each line is doing
Take a screenshot of this piece of code and the result of running the code.
You probably have used mathematical functions in algebra class, but they all had calculated values associated with them. For instance if you defined
F(x)=x2
then it follows that F(3) is 32 = 9, and F(3)+F(4) is 32 + 42 = 9 + 16 = 25.
Method calls in expressions get replaced during evaluation by the value of the method. That’s why when we can directly print out (line# 12-13) the result of the method call in the following code.
The corresponding definition and examples in C# would be the following:
1using System; //
2
3class Return1 //
4{
5 static int F(int x) //
6 {
7 return x*x; //
8 }
9
10 static void Main() //
11 {
12 Console.WriteLine(F(3)); //
13 Console.WriteLine(F(3) + F(4)); //
14 }
15}
The C# syntax you need to pay attention to is the return statement, with the word
return followed by an expression, value, or variable(s). Methods that return values
can be used in expressions (e.g., line# 13: F(3) + F(4)), just like in math class. When an
expression with a method call is evaluated, the method call is
effectively replaced temporarily by its returned value. Inside the
C# method, the value to be returned is given by the
expression in the return statement.
Since the method returns data, and all data in C# is typed,
there must be a type given for the value returned. Note that the
method header does not start with static void.
In place of void is int. The void in earlier method header
meant nothing was returned. The int here means that a value is
returned and its type is int.
After the method F finishes executing from inside
Console.WriteLine(F(3));
it is as if the statement temporarily became
Console.WriteLine(9);
and similarly when executing
Console.WriteLine(F(3) + F(4));
the interpreter first evaluates F(3) and effectively replaces the call by the returned result, 9, as if the statement temporarily became
Console.WriteLine(9 + F(4));
and then the interpreter evaluates F(4) and effectively replaces the call by the returned result, 16, as if the statement temporarily became
Console.WriteLine(9 + 16);
resulting finally in 25 being calculated and printed.
3.5.2. Return Strings
C# methods can return any type of data, not just numbers, and
there can be any number of statements executed before the return
statement. Read, follow, and run the example program, which has string as
return type:
1using System;
2
3class Return2
4{
5 static string LastFirst(string firstName, string lastName)
6 {
7 string separator = ", ";
8 string result = lastName + separator + firstName;
9 return result;
10 }
11
12 static void Main()
13 {
14 Console.WriteLine(LastFirst("Benjamin", "Franklin"));
15 Console.WriteLine(LastFirst("Andrew", "Harrington"));
16 }
17}
18
19// ** write your answer here **
To make sure you can follow the flow of execution with methods and return values, do the following:
Find the line number(s) for each step of code execution of the preceding code as the table below.
In the chart below, match the steps with the line numbers in the program above, comma-separated with one space, as a comment at the end of the code. To denote multiple lines, use dash.
Screenshot your code and the result of execution.
# |
Step |
|---|---|
1 |
Start at Main |
2 |
call the method, remembering where to return |
3 |
pass the parameters: firstName = “Benjamin”; lastName = “Franklin” |
4 |
Assign the variable separator the value “, “ |
5 |
Assign the variable result the value of lastName + separator + firstName which is “Franklin” + “, “ + “Benjamin”, which evaluates to “Franklin, Benjamin” |
6 |
Return “Franklin, Benjamin” |
7 |
Use the value returned from the method call so the line effectively becomes Console.WriteLine(“Franklin, Benjamin”);, so print it. |
8 |
call the method with the new actual parameters, remembering where to return |
9 |
pass the parameters: firstName = “Andrew”; lastName = “Harrington” |
10 |
… calculate and return “Harrington, Andrew” |
11 |
Use the value returned by the method and print “Harrington, Andrew” |
3.5.3. Return Formatted String
Perform the following for this part of the lab: - Read the description. - Copy the code to a project called Addition2a. - Run the code. - Change variable name a and b to num1 and num2. - Run the code. - Does changing the variable names affect the code execution? Why? Explain in the last line of the code.
It is common to want to construct and immediately print a string,
so having Console.Write is definitely handy when we want it.
However, sometimes we just want to have the resulting string returned,
so that we can do something else with it. We can use
the C# library method string.Format, which does just what we want:
The parameters have the same form as for Console.Write,
but the formatted string is returned.
1using System;
2
3class Addition2a
4{ // start function chunk
5 static string SumProblemString(int x, int y) // with string.Format
6 {
7 int sum = x + y;
8 return string.Format("The sum of {0} and {1} is {2}.", x, y, sum);
9 }
10 // end function chunk
11 static void Main()
12 {
13 Console.WriteLine(SumProblemString(2, 3));
14 Console.WriteLine(SumProblemString(12345, 53579));
15 Console.Write("Enter an integer: ");
16 int a = int.Parse(Console.ReadLine());
17 Console.Write("Enter another integer: ");
18 int b = int.Parse(Console.ReadLine());
19 Console.WriteLine(SumProblemString(a, b));
20 }
21}
22// ** explain here **
Note: The only caveat with string.Format is that
there is no special method corresponding to Console.WriteLine,
with an automatic terminating newline.
You can generate a newline with string.Format: Remember the
escape code "\n". Put it at the end to go on to a new line.
3.5.4. Interview String Return
Observe the following code (project name: Interview):
1using System;
2
3class Interview
4{
5 static void Main() // basic prompt/read/write example
6 {
7 Console.Write ( "Enter the interviewee's name: ");
8 string name = Console.ReadLine();
9 Console.Write( "Enter the appointment time: ");
10 string time = Console.ReadLine();
11 Console.WriteLine(name + " has an interview at " + time + ".");
12 }
13}
Modify the above program so that it accomplishes the same thing as the preceding code, but
introduce a method InterviewSentence that takes name
and time strings as parameters and returns the interview sentence string.
Follow the instructions:
Use
string.Formatin the method.Manage input from the user and output to the screen entirely in
Main.Use
InterviewSentence()to generate the sentence that you want to later print.
Take a screenshot of your code and the result of execution.
3.5.5. Birthday Method
Observe the following code:
1using System;
2
3class Birthday
4{
5 static void HappyBirthday(string person)
6 {
7 Console.WriteLine ("Happy Birthday to you!");
8 Console.WriteLine ("Happy Birthday to you!");
9 Console.WriteLine ("Happy Birthday, dear " + person + ".");
10 Console.WriteLine ("Happy Birthday to you!");
11 }
12
13 static void Main()
14 {
15 HappyBirthday("Emily");
16 HappyBirthday("Andre");
17 }
18
19}
Modify the preceding code by saving it as your
own project as BirthdayMany.cs:
Add a method call (but not another method definition), so Maria gets a verse, in addition to Emily and Andre.
Also, print a blank line between verses. (There are two ways to handle the blank lines: You may either do this by adding a print line to the method definition, or by adding a print line between all calls to the method. Recall that if you give Console.WriteLine an empty parameter list, it just goes to the next line.)
Take a screenshot of your code and result of execution.