Lesson 1.1: Hello, world

Lesson 1.1: Hello, world
Programming in C
Prof. Dr. Eike Best
Dr. Elke Wilkeit
September 28, 2002
1 #include
2
3 main()
4 {
5 printf("hello, world\n");
6 }
Exercise 1-1 (my first C program) (a) Run the ‘‘hello-world” program on
your system. Experiment with leaving out parts of the program to see what error
messagees you get. In particular, leave out the newline-escape-sequence.
Exercise 1-2a (escape sequences) Experiment to find out what happens when
printf’s argument string contains \c , where c is some character different from n.
1-2b Write a program that prints the meaning of all escape sequences. Try \\ in
order to print a single \ (this is also an escape sequence).
Exercise 1-1b (hello, world — revisited) Write a program that prints the
string ‘‘hello, world! ” in the first line, then ‘‘ello, world! h” , in the second line,
‘‘llo, world! he” in the third line, and so on, moving the first character to the end
of the string, until the original string is reached again in the last line.

Lessons 1.2, 1.3 and 1.4:
Fahrenheit and Celsius
Programming in C
Prof. Dr. Eike Best
Dr. Elke Wilkeit
September 28, 2002
1 #include
2
3 /* print Fahrenheit-Celsius table
4 for fahr = 0, 20, ..., 300 */
5 main()
6 {
7 int fahr, celsius;
8 int lower, upper, step;
9
10 lower = 0; /* lower limit of temperature table */
11 upper = 300; /* upper limit of temperature table */
12 step = 20; /* step size */
13
14 fahr = lower;
15 while (fahr

Exercise 1-3. (heading) Modify the temperature conversion program to print
a heading above the table. The first column of the table should be four characters
wide and have no decimal point and no fraction digits. The second column should
be eight characters wide and should have two fraction digits.
Exercise 1-4 (conversion) Write a program to print the correponding Celsius
to Fahrenheit table. Choose another layout than in Exercise 1-3.
1 #include
2
3 main()
4 {
5 int fahr;
6
7 for (fahr = 0; fahr

Lesson 1.5:
Character input and output (1/3)
Programming in C
Prof. Dr. Eike Best
Dr. Elke Wilkeit
September 28, 2002
1 #include
2
3 /* copy input to output; 1st version */
4 main()
5 {
6 int c;
7
8 c = getchar();
9 while (c != EOF) {
10 putchar(c);
11 c = getchar();
12 }
13 }
1 #include
2
3 /* copy input to output; 2nd version */
4 main()
5 {
6 int c;
7
8 while ((c =getchar()) != EOF)
9 putchar(c);
10 }
Exercise 1-6. (EOF) Verify that the expression getchar() != EOF is 0 or 1.
Exercise 1-7. (EOF again)
Write a program to print the value of EOF.

Lesson 1.5:
Character input and output (2/3)
Programming in C
Prof. Dr. Eike Best
Dr. Elke Wilkeit
September 28, 2002
1 #include
2
3 /* count characters in input; 1st version */
4 main()
5 {
6 long nc;
7
8 nc = 0;
9 while (getchar() != EOF)
10 ++nc;
11 printf("%ld\n", nc);
12 }
1 #include
2
3 /* count characters in input; 2nd version */
4 main()
5 {
6 double nc;
7
8 for (nc = 0; getchar() != EOF; ++nc)
9 ;
10 printf("%.0f\n", nc);
11 }
1 #include
2
3 /* count lines in input */
4 main()
5 {
6 int c, nl;
7
8 nl = 0;
9 while ((c = getchar()) != EOF)
10 if (c == ’\n’)
11 ++nl;
12 printf("%d\n", nl);
13 }
Exercise 1-8. (Counting)
Write a program to count blanks, tabs, and newlines.
Exercise 1-9. (Copying and replacing) Write a program to copy its input to
its output, replacing each string of one or more blanks by a single blank.

Lesson 1.5:
Character input and output (3/3)
Programming in C
Prof. Dr. Eike Best
Dr. Elke Wilkeit
September 28, 2002
Exercise 1-10. (More copying and replacing) Write a program to copy its
input to its output, replacing each tab by \t, each backspace by \b, and each
backslash by \\. This makes tabs and backspaces visible in an unambiguous way.
1 #include
2
3 #define IN 1 /* inside a word */
4 #define OUT 0 /* outside a word */
5
6 /* count lines, words, and characters in input */
7 main()
8 {
9 int c, nl, nw, nc, state;
10
11 state = OUT;
12 nl = nw = nc = 0;
13 while ((c = getchar()) != EOF) {
14 ++nc;
15 if (c == ’\n’)
16 ++nl;
17 if (c == ’ ’ || c == ’\n’ || c == ’\t’)
18 state = OUT;
19 else if (state == OUT) {
20 state = IN;
21 ++nw;
22 }
23 }
24 printf("%d %d %d\n", nl, nw, nc);
25 }
Exercise 1-11. (Testing) How would you test the word count program? What
kinds of inputs are most likely to uncover bugs if there are any?
Exercise 1-12. (Reformatting)
per line.
Write a program that prints its input one word

Lesson 1.6:
Arrays
Programming in C
Prof. Dr. Eike Best
Dr. Elke Wilkeit
September 28, 2002
1 #include
2
3 /* count digits, white space, others */
4 main()
5 {
6 int c, i, nwhite, nother;
7 int ndigit[10];
8
9 nwhite = nother = 0;
10 for (i = 0; i < 10; ++i)
11 ndigit[i] = 0;
12
13 while ((c = getchar()) != EOF)
14 if (c >= ’0’ && c

Lesson 1.7:
Functions
Programming in C
Prof. Dr. Eike Best
Dr. Elke Wilkeit
September 28, 2002
1 #include
2
3 int power(int m, int n);
4
5 /* test power function */
6 main()
7 {
8 int i;
9
10 for (i = 0; i < 10; ++i)
11 printf("%d %d %d\n", i, power(2,i), power(-3,i));
12 return 0;
13 }
14
15 /* power: raise base to n-th power; n>=0 */
16 int power(int base, int n)
17 {
18 int i,p;
19
20 p = 1;
21 for (i = 1; i

Lesson 1.8:
Arguments are call-by-value
Programming in C
Prof. Dr. Eike Best
Dr. Elke Wilkeit
September 28, 2002
1 /* power: raise base to n-th power; n>=0; version 2 */
2 int power(int base, int n)
3 {
4 int p;
5
6 for (p = 1; n > 0; --n)
7 p = p * base;
8 return p;
9 }

Lesson 1.9:
Character arrays (1/2)
Programming in C
Prof. Dr. Eike Best
Dr. Elke Wilkeit
September 28, 2002
1 while ( there is another line )
2 if ( it is longer than the previous longest )
3 save it ;
4 save its length ;
5 print longest line
Exercise 1-16. (Error-tolerant longest-line program) Revise the main routine
of the longest-line program so it will correctly print the length of arbitrarily
long lines, and as much as possible of the text.
Exercise 1-17. (Printing lines longer than 80 characters)
to print all input lines that are longer than 80 characters.
Write a program
Exercise 1-18. (Removing trailing invisibles) Write a program to remove
trailing blanks and tabs from each line of input, and to delete entirely blank lines.
Exercise 1-19. (Reversing strings) Write a function reverse(s) that reverses
the character string s. Use it to write a program that reverses its input a line at a
time.

1 #include
2 #define MAXLINE 1000 /* maximum input line size */
3
4 int getline(char line[], int maxline);
5 void copy(char to[], char from[]);
6
7 /* print longest input line */
8 main()
9 {
10 int cur_len; /* current line length */
11 int cur_max; /* maximum seen so far */
12 char cur_line[MAXLINE]; /* current input line */
13 char longest[MAXLINE]; /* longest line saved here */
14
15 cur_max = 0;
16 while ((cur_len = getline(cur_line, MAXLINE)) > 0)
17 if (cur_len > cur_max) {
18 cur_max = cur_len;
19 copy(longest, cur_line);
20 }
21 if (cur_max > 0) /* there was a line */
22 printf("%s", longest);
23 return 0;
24 }
25
26 /* getline: read a line into s, return length */
27 int getline(char s[], int limit)
28 {
29 int c, i;
30
31 for (i=0; i

Lesson 1.10:
External variables and scopes (1/2)
Programming in C
Prof. Dr. Eike Best
Dr. Elke Wilkeit
September 28, 2002
1 #include
2 #define MAXLINE 1000 /* maximum input line size */
3
4 int cur_max; /* maximum length seen so far */
5 char cur_line[MAXLINE]; /* current input line */
6 char longest[MAXLINE]; /* longest line saved here */
7
8 int getline(void);
9 void copy(void);
10
11 /* print longest input line; specialised version */
12 main()
13 {
14 int cur_len; /* current line length */
15 extern int cur_max;
16 extern char cur_line[];
17 extern char longest[];
18
19 cur_max = 0;
20 while ((cur_len = getline()) > 0)
21 if (cur_len > cur_max) {
22 cur_max = cur_len;
23 copy();
24 }
25 if (cur_max > 0) /* there was a line */
26 printf("%s", longest);
27 return 0;
28 }
29
30 /* getline: specialised version */
31 int getline(void)
32 {
33 int c, i;
34 extern char cur_line[];
35
36 for (i=0; i

43 return i;
44 }
45
46 /* copy: specialised version */
47 void copy(void)
48 {
49 int i;
50 extern char cur_line[], longest[];
51
52 i = 0;
53 while ((longest[i] = cur_line[i]) != ’\0’)
54 ++i;
55 }
Exercise 1-20. (Expanding tabs) Write a program detab that replaces tabs in
the input with the proper number of blanks to space to the next tab stop. Assume a
fixed number of tab stops, say every n columns. Should n be a variable or a symbolic
parameter?
Exercise 1-21. (Inserting tabs) Write a program entab that replaces strings
of blanks by the minimum number of tabs and blanks to achieve the same spacing.
Use the same tab stops as for detab. When either a tab or a single blank would
suffice to reach a tab stop, which should be given preference?
Exercise 1-22. (Breaking lines) Write a program to ‘fold’ long input lines into
two or more shorter lines after the last non-blank character that occurs before the
nth column of input. Make sure your program does something intelligent with very
long lines, and if there are no blanks or tabs before the specified column.
Exercise 1-23. (Removing comments) Write a program to remove all comments
from a C program. Don’t forget to handle quoted strings and character
constants properly. C comments do not nest.
Exercise 1-24. (Syntax checking) Write a program to check a C program for
rudimentary syntax errors like unbalanced parenthese, brackets and braces. Don’t
forget about quotes, both single and double, escape sequences, and comments. (This
program is hard if you do it in full generality.)
Lesson 1.10, 2nd page