This is an introductory lab on functions in C using the following scenario: Facebook has hired you to help write programs that interact with the user and his or her friends. Your boss has asked you to create an age calculator to be used when a user registers for the website. Let's introduce a few basics about functions. This may be a good review if you recently learned about functions. Vocabulary terms will be highlighted in bold and italics, then reviewed at the bottom.

Here is an example function definition :

 
      double yardsToMeters(int yards)
      {
         return yards * 0.9144;
      }

"double" is the return type
"yardsToMeters" is the function name
"yards" is the parameter ; "yards" is of type "int"
the function body consists of everything inside the curly brackets

Here is an example use of the function or function call :: yardsToMeters(4);
This function call would return 3.6576

When a function returns something, you need to use the value it returns. You could store the function's return value in a variable like this:: double answer = yardsToMeters(4);
In the above example, the variable "answer" would be assigned the value of 3.6576
Or, you could use the function's return value as the parameter in another function call, like this:: someFunctionThatAcceptsMeters(yardsToMeters(4))
or: printf("4 yards is equivalent to %.3f meters.", yardsToMeters(4));

Vocabulary Review:

A function definition has a return type, name, set of parameters enclosed in a set of parenthesis, and a body enclosed in a set of curly braces.
The first line of a function definition (i.e. all but the function body) is sometimes called the function signature or operation signature .
A function's return type and parameters can be any data type. The built-in or primitive data types that we will work with are: "short", "int", "long", "float", "double", "char"
If a function does not have any parameters, you use the keyword "void" in place of a parameter list.
If a function does not return anything, you use the keyword "void" as the return type. Functions that don't return anything are usually called procedures .
A function name can be any word consisting of letters, digits, and _. Function names (and variable names) cannot begin with a digit.
A function is only defined once, but it can be called many times.
When you call a function, you pass in values to the parameters.

Suppose Facebook wants you to create an age calculator that will approximate age based on a given birth year and the current year. Let's walk through creating a function to do this.

Based on this brief description, how many parameters will your function need?
regex ^\s*2\s*$ failed-message I'm sorry, that is not the right number of parameters. success-message You got the right number of parameters. parameters
What is the return type of your function?
regex ^\s*int\s*$ failed-message I'm sorry that is not the correct return type. Your return type should be one of the following: void, int, double, char success-message That's the correct return type. Good Job! returnType For the purpose of this exercise we will name our function getApproxAge and name our parameters birthYear and curYear in that order.

Finish the first line of the function, also known as the function header or signature. Remember you need the return type, function name, and parameters. ( , ) regex ^\s*$\s*\s*,\s*$\s*$ failed-message It doesn\'t look like you entered anything new. You need to type the return type, function name, and parameters in the box above. success-message firstLine regex ^\s*getApproxAge\s*$[\w\s]*\s*$ failed-message It looks like you got the function name but forgot the return data type. success-message firstLine regex ^\s*[^\(]*\(\s*birthYear[\w\s]*$ failed-message Don't forget the parameter data types. success-message firstLine regex ^\s*[^,]*,\s*curYear\s*$\s*$ failed-message Don't forget the parameter data types. success-message firstLine regex ^\s*[^$]*\(\s*int\s*,[\w\s]*$ failed-message Don't forget the parameter names. success-message firstLine regex ^\s*[^,]*,\s*int\s*$\s*$ failed-message Don't forget the parameter names. success-message firstLine regex ^\s*int\s*$\s*,\s*$\s*$ failed-message You got the return data type. Now add the function name and parameters. success-message firstLine regex ^\s*int\s*getApproxAge\s*$\s*,\s*$\s*$ failed-message You got the function name and return data type. Now add the parameters. success-message firstLine regex ^\s*int\s*getApproxAge\s*$\s*int\s*birthYear\s*,\s*$\s*$ failed-message You are getting close. Now add the second parameter. success-message firstLine regex ^\s*int\s*getApproxAge\s*$\s*,\s*int\s*curYear\s*$\s*$ failed-message You are getting close. Now add the first parameter. success-message firstLine regex ^\s*int\s*getApproxAge\s*$\s*int\s*birthYear\s*,\s*int\s*curYear\s*$\s*$ failed-message success-message Good Job! firstLine Now let's write some examples for our function.
Enter values for the parameters, and corresponding expected return values to predict the output of our function. Remember that we are just approximating age, so don't worry about what month it is and whether the birthday has not yet occurred.
The first row of the table has been completed for you as an example. Fill in the remaining rows. Birth Year Current Year Expected Output 1990 2010 20 equation test1b - test1a expected test1c failed-message I'm sorry, your 1st row of input is incorrect. success-message test1a test1b test1c equation test2b - test2a expected test2c failed-message I'm sorry, your 2nd row of input is incorrect. success-message test2a test2b test2c equation test3b - test3a expected test3c failed-message I'm sorry, your 3rd row of input is incorrect. success-message Good Job! test3a test3b test3c Let's convert some of your examples into test cases with function calls.
We will use a special function named "checkit_int" that knows how to run tests for us. This "checkit_int" function is already defined for you in a library called "checkit.h". There are many forms of "checkit" for many different data types. For instance, there is "checkit_double", "checkit_int", "checkit_char", and "checkit_string". In general, you pass two values to "checkit_int": an expected value and an actual value.
For example, here are some tests that should pass:


        checkit_int(6, 2*3)
        checkit_char('c', 'c')
        checkit_double(2.5, 5 / 2)

Here are some silly tests that should fail (you would never write tests like this because they don't make any sense):


        checkit_int(7, 2*3)
        checkit_char('c', 'd')

As you will learn later, computers handle floating point numbers in an interesting way. As a result, we normally check to see if two double's are close rather than exactly equal. The question is "how close?" The function checkit_double uses a delta (a positive number that indicates "how close" two numbers need to be to be considered equal). Here are some examples:
Now, let's create some tests with checkit_int for your getApproxAge function. Test # Expected Value Actual Value 1 checkit_int( 20 , getApproxAge(1990,2010) ) 2 checkit_int( , ) 3 checkit_int( , ) 4 checkit_int( , ) 5 checkit_int( , ) functionCode int getApproxAge(int birthYear, int curYear) { return curYear - birthYear; } functionCall @testActual2a expectedOutput @testExpected2a smessage Good job, your row 2 test passed! fmessage I'm sorry, your row 2 test failed. testExpected2a testActual2a functionCode int getApproxAge(int birthYear, int curYear) { return curYear - birthYear; } functionCall @testActual3a expectedOutput @testExpected3a smessage Good job, your row 3 test passed! fmessage I'm sorry, your row 3 test failed. testExpected3a testActual3a functionCode int getApproxAge(int birthYear, int curYear) { return curYear - birthYear; } functionCall @testActual4a expectedOutput @testExpected4a smessage Good job, your row 4 test passed! fmessage I'm sorry, your row 4 test failed. testExpected4a testActual4a functionCode int getApproxAge(int birthYear, int curYear) { return curYear - birthYear; } functionCall @testActual5a expectedOutput @testExpected5a smessage Good job, your row 5 test passed! fmessage I'm sorry, your row 5 test failed. testExpected5a testActual5a
Now finish the body of our function.
The body should calculate the approximate age, based on our two parameters. Try to do it in a single return statement.
int getApproxAge(int birthYear, int curYear) { } functionCode @functionbody functionCall getApproxAge(1990,2010) expectedOutput 20 smessage Good job, your code passed a test! fmessage I'm sorry, your failed a test. functionbody functionCode @functionbody functionCall getApproxAge(1990,2015) expectedOutput 25 smessage Good job, your code passed a test! fmessage I'm sorry, your failed a test. functionbody functionCode @functionbody functionCall getApproxAge(2006,2008) expectedOutput 2 smessage Good job, your code passed a test! fmessage I'm sorry, your failed a test. functionbody Great job! As you probably noticed, our age approximating function isn't very accurate because it only uses years. What if someone was born in December, 1990, but it is currently November 2010? Our age approximator says they are 20, but they are really only 19 years old.

Let's make a better approximation of someone's age by using both the year and the month (don't worry, we will add in the day later).
For the purpose of this exercise we will name this new function getApproxAge2.

Your return type is still an integer, but how many parameters will your new function need?
regex ^\s*4\s*$ failed-message I'm sorry that is not the right number of parameters. Remember we are using a year and month for both the current year and the birth year. success-message Good Job! parameters2 Let's write some tests for our function.
The first row has been filled out for you as an example.
Birth Year Current Year Birth Month Current Month Expected Output 1990 2010 6 7 20 functionCode int ageCalculator(int bYear, int cYear, int bMonth, int cMonth) { if(bMonth == cMonth) { return cYear-bYear; } else { return (cYear-bYear) - (bMonth/cMonth); } } functionCall ageCalculator(@test4a, @test4b, @test4c, @test4d) expectedOutput @test4e smessage fmessage I'm sorry, the 2nd row is incorrect. test4a test4b test4c test4d test4e functionCode int ageCalculator(int bYear, int cYear, int bMonth, int cMonth) { if(bMonth == cMonth) { return cYear-bYear; } else { return (cYear-bYear) - (bMonth/cMonth); } } functionCall ageCalculator(@test5a, @test5b, @test5c, @test5d) expectedOutput @test5e smessage fmessage I'm sorry, the 3rd row is incorrect. test5a test5b test5c test5d test5e functionCode int ageCalculator(int bYear, int cYear, int bMonth, int cMonth) { if(bMonth == cMonth) { return cYear-bYear; } else { return (cYear-bYear) - (bMonth/cMonth); } } functionCall ageCalculator(@test6a, @test6b, @test6c, @test6d) expectedOutput @test6e smessage Good Job! fmessage I'm sorry, the 4th row is incorrect. test6a test6b test6c test6d test6e Now write the function getApproxAge2 to calculate an approximate age using the birth and current months and years. Refer to the parameters as birthYear, curYear, birthMonth and curMonth in that order.

functionCode @betterAge functionCall getApproxAge2(1980, 2010, 6, 1) expectedOutput 29 smessage Good Job! fmessage I'm sorry, your better age calculator does not work properly. Please review the specifications. betterAge We will now write a function that will calculate the exact age of the person. Since we are now including the birth day and current day...
How many parameters will your function need? regex ^\s*6\s*$ failed-message I'm sorry that is not the right number of parameters. success-message Good Job! parameters4 First let's write some tests for our function.
Complete the following table. Note that some of the entries have been completed or partially completed for you. Birth Year Current Year Birth Month Current Month Birth Day Current Day Expected Output (Age) 1990 2010 6 6 2 3 20 1985 2010 5 5 3 1 regex ^\s*24\s*$ failed-message I'm sorry, the expect output you entered for row 2 is incorrect. success-message test7 functionCode int getAge(int birthYear, int curYear, int birthMonth, int curMonth, int birthDay, int curDay) { int current = curYear*10000 + curMonth*100 + curDay; int birth = birthYear*10000 + birthMonth*100 + birthDay; return (current - birth)/10000; } functionCall getAge(@test8a, @test8b, @test8c, @test8d, @test8e, @test8f) expectedOutput @test8g smessage fmessage I'm sorry, the 3rd row of the table is incorrect. test8a test8b test8c test8d test8e test8f test8g functionCode int getAge(int birthYear, int curYear, int birthMonth, int curMonth, int birthDay, int curDay) { int current = curYear*10000 + curMonth*100 + curDay; int birth = birthYear*10000 + birthMonth*100 + birthDay; return (current - birth)/10000; } functionCall getAge(@test9a, @test9b, @test9c, @test9d, @test9e, @test9f) expectedOutput @test9g smessage fmessage I'm sorry, the 4th row of the table is incorrect. test9a test9b test9c test9d test9e test9f test9g functionCode int getAge(int birthYear, int curYear, int birthMonth, int curMonth, int birthDay, int curDay) { int current = curYear*10000 + curMonth*100 + curDay; int birth = birthYear*10000 + birthMonth*100 + birthDay; return (current - birth)/10000; } functionCall getAge(@test10a, @test10b, @test10c, @test10d, @test10e, @test10f) expectedOutput @test10g smessage fmessage I'm sorry, the 5th row of the table is incorrect. test10a test10b test10c test10d test10e test10f test10g functionCode int getAge(int birthYear, int curYear, int birthMonth, int curMonth, int birthDay, int curDay) { int current = curYear*10000 + curMonth*100 + curDay; int birth = birthYear*10000 + birthMonth*100 + birthDay; return (current - birth)/10000; } functionCall getAge(@test11a, @test11b, @test11c, @test11d, @test11e, @test11f) expectedOutput @test11g smessage Good Job! fmessage I'm sorry, the 6th row of the table is incorrect. test11a test11b test11c test11d test11e test11f test11g Now write the function to calculate the exact age of a person when given their birth year, month, and date, as well as the current year, month, and date.
You can use this math trick to calculate age!
1. Convert inputed values into this format: YYYYMMDD
2. Subtract the birth information from the current information
3. The first three digits of your answer is the person's age. (Note that in most cases the first digit will be zero)

Example:: Birth: 19900510; Current: 20100803; Current - Birth : 0200293; First 3 Digits: 020; This person is 20 years old.

For the purposes of this exercise please name your function ageCalculator and refer to your parameters as birthYear, curYear, birthMonth, curMonth, birthDay, curDay in that order. functionCode @ageCalculator functionCall ageCalculator(1980, 2010, 6, 6, 2, 1) expectedOutput 29 smessage Good Job! fmessage Your age calculator function compiles, but it does not work properly. Please review the specifications. ageCalculator When you are done with this step, complete this survey. You will be asked to copy your program (function and tests) from this problem into the last question of the survey.

Use the C programming area on the first page of WebIDE to complete the following program. Write a function and a set of tests to solve the following problem:

Employees are paid time and a half for overtime. Overtime is any hours above 40 in a week. Write a function that accepts a total number of hours worked in a week (e.g. 45), and an hourly pay rate (e.g. 11.50). Your function should return the employee's total pay for the week, rounded down to the nearest dollar. You may assume that both parameters will be positive.

Be sure that your tests thoroughly test your function.

Congratulations! You made it to the end.