EECS2031 Lab 4 Solved

LAB 4 C preprocessing, string and other library functions. 2D arrays, Pointer basics.

In this lab you are going to practice using some C library functions. The functions covered in week 4’s lecture and earlier are listed below:

<stdio.h>

printf()
scanf()

getchar()
putchar()

sscanf()
sprintf()

fgets()
fputs()

<string.h>

int strlen(s)
s   strcpy(s,s)
s   strcat(s,s)
int strcmp(s,s)

<ctype.h>

int islower(int)
int isupper(int)
int isalpha(int)
int isdigit(int)
int isxdigit(int)

int tolower(int)
int toupper(int)

For exact prototypes of these functions, you can 1) issue ‘man 3 function_name’ in the terminal. 2) look at Appendix B of the textbook. 3) look at week4’s slides 4) google search 3 lk at Appendix B of the
You are encouraged to use these functions when appropriate, especially string functions declared in <string.h> as well as string-related IO functions declared in <stdio.h>.

Don’t forget to include the corresponding header files. Moreover, if you use functions declared in <math.h>, you need to link the library by using –lm flag of gcc. That is, gcc x.c -lm

1. Problem A. Pre-processing Macro and system()

Download the file lab4marcoSys.c, compile and run it. Observe that,

• a macro SIZE is defined using #define, used as a constant to avoid magic number.
• a parameterized macro CUBE(x) is defined, to calculate the cube of parameter x;
• the CUBE macro works correctly for argument i and j but not correctly for argument i+j.

  What went wrong? You may want to examine how the macro CUBE is pre-processed. Issue gcc -E lab4marcoSys.c, which invokes gcc pre-processor only. Note that it is the code generated by the preprocessor (what you see here), not your original code, that is to be compiled. Look at the end of the screen, observe that:

  o #include<stdio.h> is replaced with the content of stdio.h, which is inserted before main(). Try to find the declarations (prototypes) of printf, scanf,

  getchar, putchar.
  One way to filter an output in Unix is to use command grep, which we will cover later in the course. Issue command gcc -E lab4marcoSys.c | grep printf to search for lines that contain word printf. You will also see declarations of sprintf and fprintf that we mentioned in class. Then issue gcc -E lab4marcoSys.c | grep -w printf to do a ‘whole word only’ search. Do the same search for scanf.

<stdlib.h>

double atof(s) int atoi(s) long atol(s) int rand() int abs(int) system(s) exit()

<math.h>

sin() cos()
double exp(x)
double log(x)
double pow(x,y)
double sqrt(x)
double ceil(x)
double floor(x)

1

o the commented code is removed
o macro #define SIZE was processed (removed). SIZE in main() is replaced with 10; o #define CUBE is processed. CUBE (i) is textually replaced with i * i * i; and

CUBE (j) is textually replaced with j * j * j;
o macro CUBE (i + j) is textually replaced with i + j * i + j * i + j;

Modify the macro to fix the problem. You should get 343 for CUPE(i+j). After you made modifications to macro CUBE, you might want to run gcc -E lab4marcoSys.c again to see how the modified macro CUBE is processed by the preprocessor.
You can also comment out the first line #include<stdio.h>, and run preprocessing again. Now the output is much shorter, since now no header file is inserted.

Next, uncomment the 2nd line #include <stdlib.h>, and uncomment the commented block at the end of file.
The code block calls a standard library function system(), whose prototype is given in stdlib.h. Taking as input a string command, which is a valid Unix command, system executes a Unix shell command specified in command.

Compile and run it. Observe that,

• the current directory is listed, and new directories xxx and xxx/xxx2 were created in the

  current directory, and the current directory is listed again.

• predefined Macro __FILE__, __LINE__, __DATE__, __TIME__ , which contain

  the information about the current file, current date and time, are used. These information is

  useful for debugging programs.
  Issue commands in the terminal to verify that xxx and xxx/xxx2 are generated for you. Remove these directories then (how to do that in command line?) with rmdir xxx or rm – r xxx
  Submit your program using submit 2031Z lab4 lab4marcoSys.c

  2. Problem B Character array, char and math library function
  2.1 Specification
  Standard library defines a library function atoi. This function converts an array of digit characters, which represents a decimal integer literal, into the corresponding decimal integer. For example, given a char array (string) s of “134”, internally stored as , atoi(s) returns an integer 134.

  Implement your version of atoi called my_atoi, which does exactly the same conversion.

  2.2 Implementation

  Download the file lab4B.c. For each input, which is assume to be a valid integer literal, the program first prints it as a string, and then call atoi and myatoi to convert it, and output its numerical value in decimal, hex and oct, followed by double the value and square of the value. The program keeps on reading from the user until quit is entered.

  Complete the while loop in main(), and implement function my_atoi.

  Page 43 of the textbook describes an approach to convert a character array into decimal value, this approach traverses the array from left to right.
  A more intuitive approach, which you should implement here, is to calculate by traversing the array from right to left and convert following the traditional concept of

‘1’ ‘3’ ‘4’ ‘\0’ …..

…. 103 102 101 100

2

Hint: the loop body you are going to write is different from that in the textbook.

2.2 Sample Inputs/Outputs:

red 127 % a.out
Enter a word of positive number or ‘quit’: 2 2
atoi: 2 (02, 0X2) 4 4
my_atoi: 2 (02, 0X2) 4 4

Enter a word of positive number or ‘quit’: 4 4
atoi: 4 (04, 0X4) 8 16
my_atoi: 4 (04, 0X4) 8 16

Enter a word of positive number or ‘quit’: 5 5
atoi: 5 (05, 0X5) 10 25
my_atoi: 5 (05, 0X5) 10 25

Enter a word of positive number or ‘quit’: 9 9
atoi: 9 (011, 0X9) 18 81
my_atoi: 9 (011, 0X9) 18 81

Enter a word of positive number or ‘quit’: 12 12
atoi: 12 (014, 0XC) 24 144
my_atoi: 12 (014, 0XC) 24 144

Enter a word of postive number or ‘quit’: 75 75
atoi: 75 (0113, 0X4B) 150 5625 my_atoi: 75 (0113, 0X4B) 150 5625

Enter a word of positive number or ‘quit’: 100 100
atoi: 100 (0144, 0X64) 200 10000 my_atoi: 100 (0144, 0X64) 200 10000

Enter a word of positive number or ‘quit’: quit red 128 %

Submit your program using submit 2031Z lab4 lab4B.c
Once you finish, think about how to convert arrays that represent Oct or Hex integer literals. For

example “0124” (internally stored as ) and “0X12F” (stored as ).

3. Problem C String Library functions, operators, multiple files 3.1 Specification
Write an ANSI-C program that reads input from the standard input about date, and then calculate the number days that has elapsed in the year.

The program keeps on prompting user to enter Month-Date Year (three words separated by a dash and a space). For each input your program displays the days that have elapsed from the start of the year. Program terminates when user enters quit.

0 1 2 4 \0 …..

0 X 1 2 F \0 ……

3

3.2 Implementation

Download file lab4C.c and start from there. The program uses fgets() to read in a whole line. Don’t modify the existing codes.

• Implement the function int countDays(int year, int month, int day)

  which calculates how many days have elapsed since the start of the year. For simplicity, assume that there are 31 days in Jan, Mar, May, July, Sep and Nov, and there are 30 days in April, June, Aug, Oct and Dec. There are 29 days in Feb if the year is a leap year, and 28 days in Feb if the year is not leap year.

• Define function isLeap(int year)as you did for lab 2. Put the definition of this function in another file named leap.c.
• Implement the while conditions, checking if input is quit.
• Display the output as xx days of year xxx have elapsed

  Thoughts and Hints:

• How to get year, month and date information from the line of string? That is, how to

  tokenize a string? How about sscanf mentioned in class?

• In implementing countDays(), instead of checking month with lots if… elseif…

  elseif… elseif…. Or if (||…||…||…||…||…), can you use an arithmetic

  operator to simplify the code?

• When fgets reads in a line, it appends a new line character \n at the end (before \0). For

  example, input a line is stored as
  where …. are some other values (‘\0’or random values). Be careful when checking if the input is quit.

• You should not put #include “leap.c” in your main program in order to use isLeap() function. The proper way is to declare the function and compile the programs together.

  3.3 Sample Inputs/Outputs: (ONE blank link between each interaction/iteration): red 339 % a.out
  Enter ‘month-date year’: 1-1 2010
  1 days of year 2010 have elapsed

  Enter ‘month-date year’: 8-8 2011 220 days of year 2011 have elapsed

  Enter ‘month-date year’: 8-8 2012 221 days of year 2012 have elapsed

  Enter ‘month-date year’: 8-8 2016 221 days of year 2016 have elapsed

  Enter ‘month-date year’: 10-1 2010 274 days of year 2010 have elapsed

  Enter ‘month-date year’: 10-1 2012 275 days of year 2012 have elapsed

  Enter ‘month-date year’: 5-4 2017 124 days of year 2017 have elapsed

  Enter ‘month-date year’: 5-4 2012 125 days of year 2012 have elapsed

‘a’ ‘ ‘ ‘l’ ‘i’ ‘n’ ‘e’ ‘\n’ ‘\0’ ……

4

Enter ‘month-date year’: 2-12 2012 43 days of year 2012 have elapsed

Enter ‘month-date year’: 2-12 2011 43 days of year 2011 have elapsed

Enter ‘month-date year’: quit red 340 %

Assume inputs are valid.
Submit your program using submit 2031Z lab4 lab4C.c leap.c

4. Problem D String manipulations, Library functions

4.1 Specification

Develop an ANSI-C program that reads user information from the standard inputs, and outputs the modified version of the records.

4.2 Implementation

Download file lab4D.c and start from there. Note that the program

• uses loop to read inputs (from standard in), one input per line, about the user information

  in the form of name age wage, where name is a word (with no space), age is an

  integer literal, and wage is a floating point literal. See sample input below.

• uses scanf(“%s %s %s”, name, age, wage) to read in three input ‘strings’,

  where name, age and wage are of type char[20].

  The program should,

• after reading each line of inputs, creates a char [40] string resu for the modified version

  of the input. In the modified version of input, the first letter of name is capitalized, age becomes age + 10, and wage has 100% increases with 3 digits after decimal point, followed by the floor and ceiling of the increase wage. The values are separated by dashes and brackets as shown below.

  Hint: 1) to convert to a float with 3 digits after decimal point, review the code of runningAveLocal.c provided in lab3. 2) To create resu from several variables, consider sprintf. 3) if you use math library functions, be aware that the return type is double. Then you might want to either cast the double into int, or display the double

• then duplicate/copy resu to resu2 using a library function declared in <string.h> (how about strcpy or strcat)
• then duplicate/copy resu to resu3 using a library function declared in <stdio.h> (how about sprintf?)
• then output the resulting strings resu, resu2 and resu3.
• continue reading input, until a name xxx is entered (followed by any two words). (How
• check?)

  4.3 Sample Inputs/Outputs:

  red 118 % a.out
  Enter name, age and wage (xxx to quit): sue 22 33.3 Sue-32-66.600-[66,67]
  Sue-32-66.600-[66,67]
  Sue-32-66.600-[66,67]

5

Enter name, age and wage (xxx to quit): john 60 1.0 John-70-2.000-[2,2]
John-70-2.000-[2,2]
John-70-2.000-[2,2]

Enter name, age and wage (xxx to quit): lisa 30 1.34 Lisa-40-2.680-[2,3]
Lisa-40-2.680-[2,3]
Lisa-40-2.680-[2,3]

Enter name, age and wage (xxx to quit): judy 40 3.2 Judy-50-6.400-[6,7]
Judy-50-6.400-[6,7]
Judy-50-6.400-[6,7]

Enter name, age and wage (xxx to quit): xxx 2 2 red 119 %

Submit your program using submit 2031Z lab4 lab4D.c 5. Problem E. 2D array, Library functions.

5.1 Specification

Write an ANSI-C program that reads user information from the standard inputs, and outputs both the original and the modified version of the records.

5.2 Implementation

A file lab4E.c is for you to get started. The program should:

• use a table-like 2-D array (i.e., an array of ‘strings’) to record the inputs.
• use loop to read inputs (from standard in), one input per line, about the user information

  in the form of name age wage, where age is an integer literal, and wage is a floating

  point literal. See sample input below.

• store each input string into the current available ‘row’ of the 2D array, starting from row 0.
• create a modified string of the input, and store it in the next row of the 2D array. In the

  modified version of input, all letters in name are capitalized, age becomes age + 10, and wage has 50% increases and is formatted with 2 digits after decimal point.

  Hint: for converting name to upper cases, you might need a small loop to do

      name[i] = touppper(name[i])
  

• continue reading input, until a name xxx is entered.
• after reading all the inputs, output the 2-D array row by row, displaying each original input

  followed by the modified version of the input.

• display the current date and time and program name before generating the output, using

  predefined macros such as __FILE__, __TIME__ .

  •

  Note that as the partial implementation shows, you should read in the three inputs in three separate variables, but you have the choice of how they are read in: they can be read in as three ‘strings’, like in problem D, using scanf(“%s %s %s”, ….), or, you can use scanf(“%s %d %f”, ….) to read in the three inputs as string, int, float respectively.
  In the next question, you will practice reading in the whole line as a string (and then ‘tokenize’ the string). Each approach has it pros and cons.

6

Note that you will lose all marks if, instead of a 2D-array, you use 3 parallel 1-D arrays — one of names, one of ages, one for wages — to store and display information.

5.3 Sample Inputs/Outputs:

red 307 % a.out
Enter name, age and wage: john 60 1.0 Enter name, age and wage: eric 30 1.3 Enter name, age and wage: lisa 22 2.2 Enter name, age and wage: judy 40 3.22 Enter name, age and wage: xxx 2 2

Records generated in lab4E.c on Jan 26 2019 14:58:47 john 60 1.00
JOHN 70 1.50
eric 30 1.30

ERIC 40 1.95
lisa 22 2.20
LISA 32 3.30
judy 40 3.22
JUDY 50 4.83
red 308 %

Submit your program using

You should not hard-code the file name and date time.

submit 2031Z lab4 lab4E.c

6. Problem E2. 2D array, library functions.

Same question as problem E but now you read each line of input as a whole line of string.
Note that as discussed earlier, using scanf(“%s”, inputArr) does not work here, as scanf stops at the first blank (or new line character). Thus, if you enter Hi there, only Hi is read in.
As mentioned in week4’s class, in order to read a whole line of input which may contain blanks, you can use scanf(“%[^\n]s”,inputsArr),or, gets(inputsArr), but a much more common approach is to use function fgets(). Both the functions are declared in stdio.h. fgets(inputsArr, n, stdin) reads a maximum of n characters from stdin (Standard input) into inputsArr.

A file lab4E2.c is created for you to get started.
As the code shows, reading a whole line allows the input to be read into a table row directly. So you don’t need to store the original input into the table manually. The disadvantage, however, is that you have to tokenize the line in order to get the name, age and wage information.

Same output as above, except that the generated file name should be lab4E2.c, and the time is different.

Submit your program using submit 2031Z lab4 lab4E2.c 7. Problem F Pointer 101

7.1 Specification

Write your first (short) program that uses pointers.

7

7.2 Implementation

• define an integer age which is initialized to 10, define another integer age2 which is initialized to 100;
• define an integer pointer ptr that points to age
• display the value of age, both via age, and via pointer ptr ptr
• use ptr to change the value of age to 14;
• display the value of age, both via age, and via pointer ptr

*

• define another pointer ptr2, which points to age2
• copy/assign age’s value to age2 via pointer ptr and ptr2;
• display the value of age2, both via age2, and via pointer ptr2

ptr2 *

age2

ptr ptr2

• let prt2 points to age by getting the address of age from the first pointer ptr.
• use ptr2 to decrease the value of age by 1.
• display value of age, both from age, and via ptr and ptr2.

*

* age age2

• finally, display the address of age, using printf(“%p %p %p\n”,&age,ptr,ptr2);

7.3 Sample Inputs/Outputs:

red 305 % a.out
age: 10 10
age: 14 14
age2:14 14
age: 13 13 13
0x7ffd04a92bcc 0x7ffd04a92bcc 0x7ffd04a92bcc red 306

7.4 Submission:

Name your program lab4F.c and submit using
submit 2031Z lab4 lab4F.c

In summary, you should submit

You will get different numbers but they should be identical to each other.
This is the memory address of variable age, in Hex.

age