**Lab 06: Pass by reference** | COMP1633 @ MRU

Objectives

Gain experience with reference parameters
More practice designing and coding programs built out of functions
Learn how to use input redirection to test programs

Program description

When complete, this lab’s program should do the following:

Read in two times (a start time and wait time, both using a 24-hour clock)
Calculate when the wait is over
Convert that time to a 12-hour clock and display it

Setup

Update the source code for your labs repo by running the following commands in the terminal:

$ cd labs
$ git pull

January 26 update: If you haven’t run the steps to fix your labs configuration, now is a good time. Follow the instructions here .

Steps

Open by_ref.cpp, by_ref.h, and main.cpp. Copy the function header for get_time from the header file to by_ref.cpp and implement a function that reads a time entered in the format HH:MM and updates 2 reference parameters - the hours and the minutes. You can assume the data is always in the correct format.
To test this write a simple test driver main program (in main.cpp) that writes a prompt, calls the function, and prints out the time. Don’t worry about formatting - just use a simple cout.
Modify main so it also prompts for a waiting time, calls the get_time function to read the wait time, and prints it out (mostly to confirm things are working).

Now implement the function calc_end_time. This function receives 4 input parameters (hours and mins for start time and wait time) and updates 2 reference parameters (hours and mins for the end time). The time returned must be valid in 24 hour time (e.g. if you start at 23:30 and wait 2:15, the end should be 1:45).
This is the function that is assessed for the lab! From now on, this yellow box highlights the assessed code.

Modify main to call calc_end_time (and print out the end time after the call)
Implement the function convert_12hour, which is given a reference to the hours in 24-hour format. This function should update the hours parameter to represent the time in a 12-hour format. It should also update a parameter which will contain 'A' or 'P' for AM or PM respectively.
Hint: think about how you would cycle around the clock - the modulo operator might be handy! You will need an if statement for the AM/PM part though.
Modify main to call convert_12hour and print out the result as follows:
```
Finish at 7:25PM
```
To test your complete program, create a text file called time.txt. It should just contain 2 lines as follows:
```
17:45
1:40
```
Use this file as the source of input (rather than having to enter it from the keyboard) by using a feature of Linux called input redirection. This is a useful way to saving test input, so that you don’t need to retype it each time you run a program.
To use input redirection, run your program as follows:
```
$ ./main < time.txt
```

Lab Assessment

As in the previous lab, there is a unit test associated with this lab. To run it, cd up a directory to your top-level labs repository and recompile the test program:

$ cd ..
$ make lab=by_ref

This will both compile and run the test program. Note that this has also changed from last week, as I realized that there are more problems caused by trying to run the tests for all labs at once.

January 26 update: If you haven’t run the steps to fix your labs configuration, now is a good time. Follow the instructions here .