Computer Science I

Lab 2.0 - Basics

School of Computing
College of Engineering
University of Nebraska-Lincoln

This lab introduces you to the basics of a C program including fundamental variable types, arithmetic operators, standard input/output, and non-interactive input.

Prior to Lab

Before attending this lab:

1. Read and familiarize yourself with this handout.

2. Read the required chapters(s) of the textbook as outlined in the course schedule.

Peer Programming Pair-Up

For students in online section(s): you may complete the lab on your own if you wish or you may team up with a partner of your choosing, or, you may consult with a lab instructor to get teamed up online (via Zoom).

For students in the on campus section: your lab instructor may team you up with a partner.

To encourage collaboration and a team environment, labs are be structured in a peer programming setup. At the start of each lab, you will be randomly paired up with another student (conflicts such as absences will be dealt with by the lab instructor). One of you will be designated the driver and the other the navigator.

The navigator will be responsible for reading the instructions and telling the driver what to do next. The driver will be in charge of the keyboard and workstation. Both driver and navigator are responsible for suggesting fixes and solutions together. Neither the navigator nor the driver is "in charge." Beyond your immediate pairing, you are encouraged to help and interact and with other pairs in the lab.

Each week you should alternate: if you were a driver last week, be a navigator next, etc. Resolve any issues (you were both drivers last week) within your pair. Ask the lab instructor to resolve issues only when you cannot come to a consensus.

Because of the peer programming setup of labs, it is absolutely essential that you complete any pre-lab activities and familiarize yourself with the handouts prior to coming to lab. Failure to do so will negatively impact your ability to collaborate and work with others which may mean that you will not be able to complete the lab.

Lab Objectives & Topics

At the end of this lab you should be familiar with the following

• Using command line arguments

• How to declare and use variables

• Basic primitive data types

• How to choose appropriate data types for a given problem

Activities

Using Command Line Arguments

When you run a program from the command line, you can also provide the program with arguments that the program can use for input or for configuration. To understand this, we have provided you two completed C programs that compute an age given a birthdate. The first works by prompting the user for input interactively, while the second uses command line arguments.

Instructions

1. Go to your labs directory and clone the Lab 2.0 project from GitHub by executing the following command:
   git clone https://github.com/cbourke/CSCE155-C-Lab02

2. Change your directory to the cloned project and open and view the source files, but do not make any changes.

3. Compile the first program using gcc birthday.c and run it using ./a.out answer the questions in the worksheet.md file (type your answers in this file).

4. Compile the second version using: gcc birthday_cli.c. The second program is non-interactive: it reads input directly from the command line when you run it, so run it as ./a.out Dennis 1941 9 9

5. Run the program and answer the questions in your worksheet

Basic Data Types

A variable is a name associated with a memory cell whose value can change. When variables are stored in memory, the computer has to have a way of knowing what type of data is stored in a given variable. Data types identify the type of values stored in a memory location and operations that can be performed on those values. A computer will not use the same amount of memory to store a single letter as it does to store a very large real number, and the values are not going to be interpreted the same way. Therefore, different data types may have different sizes. The (incomplete) table in question 4 on the worksheet shows some basic data types with their sizes and ranges. Size is represented in bytes. A byte is a unit of storage capable of holding a single character. A byte is usually considered equal to 8 bits. A bit (short for binary digit), is the smallest unit of information in a computer--either a zero or a one. Some basic data types can be either signed (either positive or negative) or unsigned (non-negative).

Instructions

The sizes and ranges of data types depend on the system the program is compiled for. We will explore the sizes of each of the primitive types defined in C on the CSE system. You have been provided a source file, ranges.c that outputs the sizes of each of the basic types.

1. Compile the source file: gcc ranges.c

2. Run your program: ./a.out

3. Complete the table provided in your worksheet

Currency Conversion

Write a program that will convert US Dollars to British Pounds (GBP) and Japanese (JPY). 10% of the total amount of US Dollars will be taken as an exchange fee. For the rest of the US Dollars, half will be changed to British Pounds and the other half to JPY. Assume the exchange rate is: 1 US Dollar = 0.79 British Pound; 1 US Dollar = 127.65 JPY. The program should ask the user to input the amount of US dollars then print an appropriate output. Both GBP and dollar units should be output to two decimal points. However, Yen are not divisible units so its output should only be a whole number.

An example run would look something like the following:

Please input the total amount of US Dollars: 100.00
Fee (10%): $10.00
You get:
35.55 GBP
5744 JPY

Instructions

1. Create a new source file named dollar.c

2. Write your complete C program in this source file, be sure to choose appropriate data types for your variables

3. Compile and run your program as before:

   gcc dollar.c
   ./a.out
   

4. Test your program and answer the questions in your worksheet

Mixed types

A mixed-type expression is an expression with operands of different data types. When an assignment statement is executed, the expression on the right-hand-side is evaluated, and then the resulting value is placed into the variable on the left-hand-side. For example:

int x = (8 * 4) + (3 * .5);

The data types of the operand affect the data type of the result. This can lead to some initially unintuitive results. When performing division between two integers, the result is necessarily an integer. For example:

int a = 10, b = 20, c;
c = a / b;

In the code snippet above, the floating point result of 10 / 20 should be 0.5, but the actual value stored in the variable c is zero! This is because the result of an operation of two integers is an integer: thus the decimal part of the result is truncated (dropped). We could fix this by making at least one of the operands (and the resulting variable) a floating point variable through type-casting:

int a = 10, b = 20;
double c;
c = (double) a / b;

You have been given a C program, area.c that reads in the base and the height of a triangle and calculates the total area.

1. Read through and understand the source code

2. Compile and run your program to answer the remaining questions in your worksheet.

3. Using the previous birthday programs as a reference, change the area program to accept command line arguments instead of prompting for input.

   Command line inputs are communicated through the **argv (argument "vector") parameter in the main function (which is an array of strings). Each argument can be accessed by indexing this array with zero being the first index (so the arguments are stored in argv[0], argv[1], etc.). The first argument is always the executable's file name, so the first actual argument starts at index 1. To convert these strings to numeric values you can use the conversion functions in the standard library:

   int a = atoi(argv[1]);
   double b = atof(argv[2]);

Handin/Grader Instructions

1. Hand in your completed files:

   • dollar.c

   • area.c

   You should have completed your worksheet, but you won't be handing it in. Be sure your program(s) pass all tests to get credit.

2. Even if you worked with a partner, you both should turn in all files.

Advanced Activities (Optional)

Modify the birthday_cli program to validate the input data. It should check for any invalid dates and if the user inputs bad data, it should quit with an error message.