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LAB 1 Introduction to C

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LAB 1
Introduction to C, Function Declaration vs. Definition, Basic I/O
(scanf/printf, getchar/putchar, input/output redirection)

Pre-lab exercise:
Review the videos and instructions regarding coding environments for C, and decide your coding
environment, e.g., work locally, and then transfer to the lab, or, work in the lab environment
directly. If you cannot decide, contact the instructor for a tailored solution.
Problem 0 printf() in Java (5 pts)
Specification
While this is a course on C programming, let’s start our very first lab with a JAVA exercise.
Download the partially implemented Java program Hello.java . This program reads a name
and an integer from the user, then outputs the double and triple value of the entered integer.
Implementation
• First, complete the println() statement, so that it produces the output as shown below.
Don’t add new lines in the program. Do all the formatting in println(). Probably you
need to use string concatenations + multiple times in println().
• Next, complete the printf() statement so that it produces the same output, as shown
below. Do not use string concatenations in printf, i.e., don’t use + . Again, don’t add new
lines of code. Do the printing in one call to printf().
Objectives
The purpose of this exercise is for you to:
• be aware that printf also exists in JAVA (actually JAVA borrows the idea from C)
• learn the syntax of printf in JAVA and C (the formatting syntax are the same)
• observe that sometimes using printf is easier than println, the code is cleaner (IMHO)
• be aware that Java program can be compiled and run in command-line (as shown in class)
Sample Inputs/Outputs: (Don’t use an IDE such as Eclipse) In a terminal, navigate to
the directory where the Java file is located. E.g., if you have created a directory 2031 on your
lab home directory, and a sub-directory lab1 in directory 2031, and develop the programs
there, then navigate to the directory by issuing cd 2031/lab1
red 300 % javac Hello.java
red 301 % java Hello
Please enter the name: Judy
Please enter the number: 22
Hi Judy, input is 22. Double and triple of 22 is 44 and 66, respectively
Hi Judy, input is 22. Double and triple of 22 is 44 and 66, respectively
red 302 % java Hello
Please enter the name: Joe
run java program in command_line
compile java program in command_line
in command_line
red xxx % is
the terminal
prompt if you
login to the
red server
using ssh.
If you use the
Remote lab
connection,
your prompt
would be
eaYY xxx%
where YY is
the terminal id
that you chose.
2
Please enter the number: 100
Hi Joe, input is 100. Double and triple of 100 is 200 and 300, respectively
Hi Joe, input is 100. Double and triple of 100 is 200 and 300, respectively
red 303 %
Submission (from lab):
Problem 0 scanf, printf() in C (5 pts)
Specification
Write the C version of the Hello program which, similar to the Java program, asks for a number
and then outputs the double and triple of the number. Note that the C program does not ask for
name (we haven’t learnt how to store strings.)
Name the program hello.c Since this may be the very first C program you write, if you have
difficulties getting started, see the provided c files and instructions for other questions for hints.
Sample Inputs/Outputs:
red 331 % gcc hello.c
red 332 % a.out
Please enter the number: 23
Hi, input is 23. Double and triple of 23 is 46 and 69, respectively.
red 333 %
Submission (from lab):
In a lab terminal, navigate to the directory where your file is located, and then issue the
command red 310 % submit 2031A lab1 hello.c

1 problem A scanf(), printf() in C
Specification
Download program scanf2.c, which takes two inputs from standard input (default: keyboard),
and outputs the sum of the two numbers to standard output (default: screen). (This is the
program shown in class and slides). Read the code and observe that,
• we specify what the input should “look like” in the formatting string of scanf. Here the
formatting string “%d %d” indicates that scanf expects two integers separated by blank.
• in order to store the input values into variable a and b, we need to use &a and &b as
additional arguments of scanf. We will explain later why & is needed.
• printf also uses %d for integer conversion. A conversion specification %d in the formatting
string will be replaced/filled by a value of type int, which can be either an integer constant
such as 32, or an int variable, or a function call which returns an int. Note that unlike in
scanf, here no & is used in front of variable names.
• there is a \n at the end of the formatting string of the last printf statement, whereas
there is no \n at the end of the formatting string of the first print statement.
Compile and run the program with different inputs. Try valid inputs such as
3 45
50 125
red 310 % submit 2031A lab1 Hello.java
In a lab terminal, navigate to the directory where your file is located, and then issue the
command
You may need ./a.out if you work
outside the lab environment.
3
Also try some invalid inputs such as
3 4.5
4.7 3
4 A
and observe that variable a or b or both cannot get correct number from the user. Also try to
delete the \n in the formatting string of the last printf statement, see what happens. Try to
add \n to the first printf statement, see what happens.
Next, modify the program so that it takes as input two integers separated by <><><>.
Sample input and outputs
red 306 % gcc scanf2.c
red 307 % a.out
Enter two integers separated by <><><>: 4<><><>32
Entered 4 and 32, Sum is 36.
red 308 % a.out
Enter two integers separated by <><><>: 40<><><>302
Entered 40 and 302, Sum is 342.
Try some invalid inputs such as
4<><>32
4 32
4<><><>32.56
43.2<><><>3
observe that a or b or both cannot get the correct number from the user.
Finally, remove the & before a or b, then compile and run the program again. The program
compiles BUT when you run, it crashes, generating error message Segmentation fault
(core dumped). We will explain this later.
You don’t need to submit anything for this question but doing this exercise gets you better
prepared for the following questions.
2 Problem B. scanf, printf in C (10 pts)
Specification
Write an ANSI-C program that reads input from the standard input (keyboard), and then outputs
the reformatted versions of the input to standard output (screen).
Implementation
• name your program lab1B.c
• use scanf to read input (from Standard Input), which are in the form of
Month Day Year (i.e., three integers separated by white spaces).
• use printf to generate output in the form of Year/month/day and Year-month-day
• display the following prompt (leave a white space after the colon)
Enter month, day and year separated by spaces:
• display output The input ‘m d y’ is reformatted as y/m/d and y-m-d
• Note: you should do the reformatting only within printf. In particular, you should use at
most three variables, and feed them into printf judiciously. There should be only one
printf statement.
Sample Inputs/Outputs:
You may need ./a.out if you work
outside the lab environment.
4
red 306 % gcc lab1B.c
red 307 % a.out
Enter month, day and year separated by spaces: 3 20 2019
The input ‘3 20 2019 ‘ is reformatted as 2019/3/20 and 2019-3-20
red 308 % a.out
Enter month, day and year separated by spaces: 9 16 2021
The input ‘9 16 2021 ‘ is reformatted as 2021/9/16 and 2021-9-16
red 309 %
Submit your program by issuing submit 2031A lab1 lab1B.c
3 Problem C. Functions in C (10 pts)
Download the program lab1C.c, compile it using gcc lab1C.c
Observe that the compilation process fails (why?), and a.out is not generated.
Modify the program to make it compile. Note that you should not modify or move the existing
code. That is, do not modify the code of main() and sum(), and also do not move the
functions. Instead, add something to make the program compile.
Next, modify the function greet(), so that it prints Hello X! where X is the value of parameter
i, as shown in the same output.
Sample Inputs/Outputs:
red 306 % gcc lab1C.c
red 307 % a.out
Hello 2031!
Hello 1012!
2.200000 + 3.300000 = 5.500000
Submit your program by issuing submit 2031A lab1 lab1C.c
4 Problem D. Functions, scanf(), printf(), floats (10 pts)
Specification
Improve program lab1C, so that it can read two float numbers for the Standard Input,
separated by two pound (#) signs, and then output the sum of the two float numbers to
standard output.
Implementation
• name your program lab1D.c
• use scanf to read inputs (from Standard Input), which are in the form of
float1##float2 (i.e., two float numbers separated by two pound signs).
• use printf to generate output. Note that by default printf displays six digits after
decimal points of a floating point number.
Sample Inputs/Outputs:
red 338 % gcc lab1D.c -o lab1D
red 339 % lab1D
Hello 2031!
Hello 1012!
5
Enter two float numbers separated by ##: 2.35##5.64
2.350000 + 5.640000 = 7.990000
red 340 % lab1D
Hello 2031!
Hello 1012!
Enter two float numbers separated by ##: 1.2345##6.783
1.234500 + 6.783000 = 8.017500
Submit your program by issuing submit 2031A lab1 lab1D.c
5 Problem E. Simple loops in C (15 pts)
Specification
Extend program lab1D.c above, in such a way that it first prompts the user to enter an
integer number, which indicates how many times the user wants to interact with the program.
Then the program interacts with the user accordingly.
Implementation
• name your program lab1E.c
• use a loop (for or while) to interact (i.e., read input and generate output) n times,
where n is entered by the user.
• display the two inputs with 3 decimal points, and the sum with the default format followed
by 2 decimal points version
Sample Inputs/Outputs: (ONE blank line between each interaction/iteration):
red 338 % gcc lab1E.c -o lab1E
red 339 % lab1E
Hello 2031!
Hello 1012!
Enter the number of interactions: 4
Enter two float numbers separated by ##: 2.35##5.64
2.350 + 5.640 = 7.990000 (7.99)
Enter two float numbers separated by ##: 1.1##2.2
1.100 + 2.200 = 3.300000 (3.30)
Enter two float numbers separated by ##: 1.2343##6.789
1.234 + 6.789 = 8.023300 (8.02)
Enter two float numbers separated by ##: 1.2345##6.78994
1.235 + 6.790 = 8.024440 (8.02)
red 340 %
Submit your program by issuing submit 2031A lab1 lab1E.c
6. Problem F0. getchar, putchar, input/output redirection
6.1 Specification
6
Download the provided program countChar.c, which uses function getchar() to read user
input from standard input (default: keyboard) and counts the total number of characters in the
input, and outputs to standard output (default: screen). (This program is also in lecture slides.)
Play with the program and make sure you understand the program. In particular, observe a few
things about getchar:
• getchar() reads characters from standard input (stdin), which by default is the keyboard.
But standard input can be redirected (substituted) from an input file using < filename.
In the latter case getchar() will read from the input file instead.
• getchar() returns EOF (which is a special negative integer number defined in C) when
the “end of file” is reached.
o If the program reads from a text file (redirected using < ), then the end of the text file
is “end of file”;
o If the program reads from default standard in (i.e., keyboard) , then in Unix, ctrl D
indicates “end of file” (in Windows, it is ctrl Z )
• Instead of a char, function getchar returns an int. This will be explained in class.
6.2 Sample Inputs/Outputs (from Standard input – keyboard):
red 309 % gcc countChar.c
red 310 % a.out
hello
how are you
I am good
^D
# of chars: 28
red 311 % a.out
hello
how are you?
I am good and Thanks!
^D
# of chars: 41
red 312 %
6.3 Sample Inputs/Outputs (use redirected input/output files):
All the program run so far take inputs from standard in (stdin) which by default is the keyboard,
and write output to standard out (stdout) which by default is the screen.
You can always redirect the Standard in (keyboard) from an input file using <
You can always redirect the Standard out (screen) to an output file using >
Download (don’t copy and paste) file greetings.txt, whose content is
hello
how are you
I am good
red 313 % a.out < greetings.txt
# of chars: 28
This time the program does not ask you to enter anything, because standard input is
redirected/substituted from a text file, so program reads inputs from file greetings.txt
(press Ctrl and D)
7
red 314 % a.out > output.txt
hello
how are you
I am good
^D
red 315
This time the program reads inputs from user (keyboard), but nothing was generated on the
standard out (screen), because all outputs are redirected to a text file using >
Now a new file output.txt should be generated (in the current directory). Use command ls
or ls –l to confirm this. Then use command cat or more to view the content of
output.txt (If you don’t know what is happening here, please review the CSE1020 Guided
Tour or the Unix tutorial posted on the course website.)
red 316 % ls -l
red 317 % cat output.txt
# of chars: 28
Finally, issue
red 318 % a.out < greetings.txt > output2.txt
red 319 %
This time both the standard input and standard out are redirected. Thus the program reads
inputs from greetings.txt, and write outputs to output2.txt. Check the content of file
output2.txt. Also in the terminal, issue cal or date to view the output, and then issue
cal > temp.txt or date > temp.txt to see how the output is redirected to a file .
You don’t need to submit anything for this question but doing this exercise gets you prepared
for the next questions.
7. Problem F2 getchar, character comparison (15 pts)
Specification
The provided program uses getchar() to read input character by character, counting the
number of characters from the standard input (keyboard or redirected from an input file).
Modify the program so that it also counts the number of characters ‘a’ in the input.
Implementation
• Name your program countChar2.c
• Hint: you might need to compare every character getchar reads in against the character
‘a’. In Java or C, how to compare two characters?
Sample Inputs/Outputs
red 307 % gcc countChar2.c -o cc2
red 308 % cc2
hello
how are you?
I am good and Thanks!
^D
# of chars: 41
8
# of char ‘a’: 4
red 309 % cc2
hello
how are you
I am good
^D
# of chars: 28
# of char ‘a’: 2
red 310 % cc2 < greetings.txt
# of chars: 28
# of char ‘a’: 2
red 311 %
Submit your program by issuing submit 2031A lab1 countChar2.c
7. Prob F3 getchar, character comparison, special chars (15 pts)
Specification
Each input line to the above programs, either from keyboard or from the text file, ends with an
invisible new line character. The new line characters are counted in the above programs.
Modify the program countChar so that new line characters are not counted.
Implementation
• Name your program countChar3.c
• Hint: you might need to compare every character getchar reads in against the new line
character. In Java or C, how is new line character represented?
Sample Inputs/Outputs
red 318 % gcc countChar3.c -o cc3
red 319 % cc3
hello
how are you?
I am good and Thanks!
^D
# of chars: 38
red 320 % cc3
hello
how are you
I am good
^D
# of chars: 25
red 320 % cc3 < greetings.txt
# of chars: 25
Submit your program by issuing submit 2031A lab1 countChar3.c
9
8. Prob F4 getchar, character comparison, special chars (15 pts)
Modify the program countChar3.c so that it also counts the number of lines and number of
blank (space) in the input.
Name your program countChar4.c
red 308 % gcc countChar4.c -o cc4
red 309 % cc4
hello
how are you
I am good
^D
# of chars: 25 (# of blank: 4)
# of lines: 3
red 319 % cc4
hello
how are you?
I am good and Thanks!
^D
# of chars: 38 (# of blanks: 6)
# of lines: 3
red 310 % cc4 < greetings.txt
# of chars: 25 (# of blanks: 4)
# of lines: 3
red 311 % cc4 < greetings.txt > output4.txt
red 312 % cat output4.txt
# of chars: 25 (# of blanks: 4)
# of lines: 3
Submit your program by issuing submit 2031A lab1 countChar4.c
Make sure your program compiles in the lab environment. The program that does
not compile in the lab will get 0.
All submissions need to be done from the lab, using command line.
In summary, for this lab you should submit the following files:
Hello.java hello.c lab1B.c lab1C.c lab1D.c lab1E.c
countChar2.c countChar3.c countChar4.c
From any directory, you can issue submit -l 2031A lab1 to get a list of files that you
have submitted for lab1.
Also note that you can submit the same file multiple times. Then the latest file will overwrite
the old one.
lower case L
10
Common Notes All submitted files should contain the following header:
/***************************************
* EECS2031A 21SU – Lab1 *
* Author: Last name, first name *
* Email: Your email address *
* eecs_username: Your eecs login user name *
* York Student #: Your student number
****************************************/

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