典型例题
输入行排序
1 #include <stdio.h>
2 #include <string.h>
3
4 #define MAXLINES 5000 /* max #lines to be sorted */
5
6 char *lineptr[MAXLINES]; /* pointers to text lines */
7
8 int readlines(char *lineptr[], int nlines);
9 void writelines(char *lineptr[], int nlines);
10
11 void qsort(char *lineptr[], int left, int right);
12
13 /* sort input lines */
14 main()
15 {
16 int nlines; /* number of input lines read */
17
18 if ((nlines = readlines(lineptr, MAXLINES)) >= 0) {
19 qsort(lineptr, 0, nlines-1);
20 writelines(lineptr, nlines);
21 return 0;
22 } else {
23 printf("error: input too big to sort\n");
24 return 1;
25 }
26 }
27
28 #define MAXLEN 1000 /* max length of any input line */
29 int getline(char *, int);
30 char *alloc(int);
31
32 /* readlines: read input lines */
33 int readlines(char *lineptr[], int maxlines)
34 {
35 int len, nlines;
36 char *p, line[MAXLEN];
37
38 nlines = 0;
39 while ((len = getline(line, MAXLEN)) > 0)
40 if (nlines >= maxlines || p = alloc(len) == NULL)
41 return -1;
42 else {
43 line[len-1] = '\0'; /* delete newline */
44 strcpy(p, line);
45 lineptr[nlines++] = p;
46 }
47 return nlines;
48 }
49
50 /* writelines: write output lines */
51 void writelines(char *lineptr[], int nlines)
52 {
53 int i;
54
55 for (i = 0; i < nlines; i++)
56 printf("%s\n", lineptr[i]);
57 }
58 /* qsort: sort v[left]...v[right] into increasing order */
59 void qsort(char *v[], int left, int right)
60 {
61 int i, last;
62 void swap(char *v[], int i, int j);
63
64 if (left >= right) /* do nothing if array contains */
65 return; /* fewer than two elements */
66 swap(v, left, (left + right)/2);
67 last = left;
68 for (i = left+1; i <= right; i++)
69 if (strcmp(v[i], v[left]) < 0)
70 swap(v, ++last, i);
71 swap(v, left, last);
72 qsort(v, left, last-1);
73 qsort(v, last+1, right);
74 }
75 /* swap: interchange v[i] and v[j] */
76 void swap(char *v[], int i, int j)
77 {
78 char *temp;
79
80 temp = v[i];
81 v[i] = v[j];
82 v[j] = temp;
83 }
命令行参数指定查找字符串
1 #include <stdio.h>
2 #include <string.h>
3 #define MAXLINE 1000
4
5 int getline(char *line, int max);
6
7 /* find: print lines that match pattern from 1st arg */
8 main(int argc, char *argv[])
9 {
10 char line[MAXLINE];
11 int found = 0;
12
13 if (argc != 2)
14 printf("Usage: find pattern\n");
15 else
16 while (getline(line, MAXLINE) > 0)
17 if (strstr(line, argv[1]) != NULL) {
18 printf("%s", line);
19 found++;
20 }
21 return found;
22 }
函数指针
1 #include <stdio.h>
2 #include <string.h>
3
4 #define MAXLINES 5000 /* max #lines to be sorted */
5 char *lineptr[MAXLINES]; /* pointers to text lines */
6
7 int readlines(char *lineptr[], int nlines);
8 void writelines(char *lineptr[], int nlines);
9
10 void qsort(void *lineptr[], int left, int right,
11 int (*comp)(void *, void *));
12 int numcmp(char *, char *);
13
14 /* sort input lines */
15 main(int argc, char *argv[])
16 {
17 int nlines; /* number of input lines read */
18 int numeric = 0; /* 1 if numeric sort */
19
20 if (argc > 1 && strcmp(argv[1], "-n") == 0)
21 numeric = 1;
22 if ((nlines = readlines(lineptr, MAXLINES)) >= 0) {
23 qsort((void**) lineptr, 0, nlines-1,
24 (int (*)(void*,void*))(numeric ? numcmp : strcmp));
25 writelines(lineptr, nlines);
26 return 0;
27 } else {
28 printf("input too big to sort\n");
29 return 1;
30 }
31 }
32
33 /* qsort: sort v[left]...v[right] into increasing order */
34 void qsort(void *v[], int left, int right,
35 int (*comp)(void *, void *))
36 {
37 int i, last;
38
39 void swap(void *v[], int, int);
40
41 if (left >= right) /* do nothing if array contains */
42 return; /* fewer than two elements */
43 swap(v, left, (left + right)/2);
44 last = left;
45 for (i = left+1; i <= right; i++)
46 if ((*comp)(v[i], v[left]) < 0)
47 swap(v, ++last, i);
48 swap(v, left, last);
49 qsort(v, left, last-1, comp);
50 qsort(v, last+1, right, comp);
51 }
52
53 #include <stdlib.h>
54
55 /* numcmp: compare s1 and s2 numerically */
56 int numcmp(char *s1, char *s2)
57 {
58 double v1, v2;
59
60 v1 = atof(s1);
61 v2 = atof(s2);
62 if (v1 < v2)
63 return -1;
64 else if (v1 > v2)
65 return 1;
66 else
67 return 0;
68 ｝
关键字统计
1 #include <stdio.h>
2 #include <ctype.h>
3 #include <string.h>
4
5 #define MAXWORD 100
6
7 struct key {
8 char *word;
9 int count;
10 } keytab[] = {
11 "auto", 0,
12 "break", 0,
13 "case", 0,
14 "char", 0,
15 "const", 0,
16 "continue", 0,
17 "default", 0,
18 /* ... */
19 "unsigned", 0,
20 "void", 0,
21 "volatile", 0,
22 "while", 0
23 };
24
25
26 int getword(char *, int);
27 int binsearch(char *, struct key *, int);
28
29 /* count C keywords */
30 main()
31 {
32 int n;
33 char word[MAXWORD];
34
35 while (getword(word, MAXWORD) != EOF)
36 if (isalpha(word[0]))
37 if ((n = binsearch(word, keytab, NKEYS)) >= 0)
38 keytab[n].count++;
39 for (n = 0; n < NKEYS; n++)
40 if (keytab[n].count > 0)
41 printf("%4d %s\n",
42 keytab[n].count, keytab[n].word);
43 return 0;
44 }
45
46 /* binsearch: find word in tab[0]...tab[n-1] */
47 int binsearch(char *word, struct key tab[], int n)
48 {
49 int cond;
50 int low, high, mid;
51
52 low = 0;
53 high = n - 1;
54 while (low <= high) {
55 mid = (low+high) / 2;
56 if ((cond = strcmp(word, tab[mid].word)) < 0)
57 high = mid - 1;
58 else if (cond > 0)
59 low = mid + 1;
60 else
61 return mid;
62 }
63 return -1;
64 }
65 /* getword: get next word or character from input */
66 int getword(char *word, int lim)
67 {
68 int c, getch(void);
69 void ungetch(int);
70 char *w = word;
71
72 while (isspace(c = getch()))
73 ;
74 if (c != EOF)
75 *w++ = c;
76 if (!isalpha(c)) {
77 *w = '\0';
78 return c;
79 }
80 for ( ; --lim > 0; w++)
81 if (!isalnum(*w = getch())) {
82 ungetch(*w);
83 break;
84 }
85 *w = '\0';
86 return word[0];
87 }
关键字统计指针版
1 #include <stdio.h>
2 #include <ctype.h>
3 #include <string.h>
4 #define MAXWORD 100
5
6 int getword(char *, int);
7 struct key *binsearch(char *, struct key *, int);
8
9 /* count C keywords; pointer version */
10 main()
11 {
12 char word[MAXWORD];
13 struct key *p;
14
15 while (getword(word, MAXWORD) != EOF)
16 if (isalpha(word[0]))
17 if ((p=binsearch(word, keytab, NKEYS)) != NULL)
18 p->count++;
19 for (p = keytab; p < keytab + NKEYS; p++)
20 if (p->count > 0)
21 printf("%4d %s\n", p->count, p->word);
22 return 0;
23 }
24
25 /* binsearch: find word in tab[0]...tab[n-1] */
26 struct key *binsearch(char *word, struck key *tab, int n)
27 {
28 int cond;
29 struct key *low = &tab[0];
30 struct key *high = &tab[n];
31 struct key *mid;
32
33 while (low < high) {
34 mid = low + (high-low) / 2;
35 if ((cond = strcmp(word, mid->word)) < 0)
36 high = mid;
37 else if (cond > 0)
38 low = mid + 1;
39 else
40 return mid;
41 }
42 return NULL;
43 }
单链表自引用结构体
1 #include <stdio.h>
2
3 #include <stdlib.h>
4
5 #include <string.h>
6
7
8
9 #define MAXWORD 1000
10
11 struct node {
12
13 char *word;
14
15 int count;
16
17 struct node *next;
18
19 };
20
21 struct node*addlist(struct node *head, char *w);
22
23 char *strdup(char *s);
24
25 void listprint(struct node *p);
26
27
28
29 main() {
30
31 struct node *head = NULL;
32
33 char word[MAXWORD];
34
35 while(getword(word, MAXWORD)!=EOF)
36
37 if(isalpha(word[0]))
38
39 head = addlist(head, word);
40
41 listprint(head);
42
43 system("pause");
44
45 }
46
47
48
49 void listprint(struct node *p) {
50
51 while(p!=NULL) {
52
53 printf("%4d %s\n", p->count, p->word);
54
55 p = p->next;
56
57 }
58
59 }
60
61
62
63 struct node*addlist(struct node *head, char *w){
64
65 int cond;
66
67 struct node *p = head, *pre = NULL;
68
69 while(p!=NULL) {
70
71 cond=strcmp(w,p->word);
72
73 if(cond == 0) {
74
75 p->count ++;
76
77 return head;
78
79 } else if(cond > 0) {
80
81 pre = p; p = p->next;
82
83 } else
84
85 break;
86
87 }
88
89 p =(struct node*)malloc(sizeof(struct node));
90
91 p->word = strdup(w);
92
93 p->count = 1;
94
95 if(pre == NULL) {
96
97 p->next = NULL;
98
99 head = p;
100
101 } else {
102
103 p->next = pre->next;
104
105 pre->next = p;
106
107 }
108
109 return head;
110
111 }
112
113
114
115 char *strdup(char *s) {
116
117 char *p = (char *)malloc(strlen(s)+1);
118
119 strcpy(p, s);
120
121 return p;
122
123 }
124
125
126
127 #define BUFSIZE 100
128
129
130
131 char buf[BUFSIZE]; /* buffer for ungetch */
132
133 int bufp = 0; /* next free position in buf */
134
135 int getch(void) /* get a (possibly pushed-back) character */
136
137 {
138
139 return (bufp > 0) ? buf[--bufp] : getchar();
140
141 }
142
143
144
145 void ungetch(int c) /* push character back on input */ {
146
147 if (bufp >= BUFSIZE)
148
149 printf("ungetch: too many characters\n");
150
151 else
152
153 buf[bufp++] = c;
154
155 }
156
157
158
159 int getword(char *word, int lim)
160
161 {
162
163 int c;
164
165 char *w = word;
166
167
168
169 while (isspace(c = getch()))
170
171 ;
172
173 if (c != EOF)
174
175 *w++ = c;
176
177 if (!isalpha(c)) {
178
179 *w = '\0';
180
181 return c;
182
183 }
184
185 for ( ; --lim > 0; w++)
186
187 if (!isalnum(*w = getch())) {
188
189 ungetch(*w);
190
191 break;
192
193 }
194
195 *w = '\0';
196
197 return word[0];
198
199 }
变长参数列表
1 #include <stdarg.h>
2
3 /* minprintf: minimal printf with variable argument list */
4 void minprintf(char *fmt, ...)
5 {
6 va_list ap; /* points to each unnamed arg in turn */
7 char *p, *sval;
8 int ival;
9 double dval;
10
11 va_start(ap, fmt); /* make ap point to 1st unnamed arg */
12 for (p = fmt; *p; p++) {
13 if (*p != '%') {
14 putchar(*p);
15 continue;
16 }
17 switch (*++p) {
18 case 'd':
19 ival = va_arg(ap, int);
20 printf("%d", ival);
21 break;
22 case 'f':
23 dval = va_arg(ap, double);
24 printf("%f", dval);
25 break;
26 case 's':
27 for (sval = va_arg(ap, char *); *sval; sval++)
28 putchar(*sval);
29 break;
30 default:
31 putchar(*p);
32 break;
33 }
34 }
35 va_end(ap); /* clean up when done */
36 }
文件访问
1 #include <stdio.h>
2
3 /* cat: concatenate files, version 1 */
4 main(int argc, char *argv[])
5 {
6 FILE *fp;
7 void filecopy(FILE *, FILE *)
8
9 if (argc == 1) /* no args; copy standard input */
10 filecopy(stdin, stdout);
11 else
12 while(--argc > 0)
13 if ((fp = fopen(*++argv, "r")) == NULL) {
14 printf("cat: can't open %s\n, *argv);
15 return 1;
16 } else {
17 filecopy(fp, stdout);
18 fclose(fp);
19 }
20 return 0;
21 }
22
23 /* filecopy: copy file ifp to file ofp */
24 void filecopy(FILE *ifp, FILE *ofp)
25 {
26 int c;
27
28 while ((c = getc(ifp)) != EOF)
29 putc(c, ofp);
30 }
选择题
下列程序执行后的输出结果是 A 6 B 7 C 8 D 9
下列程序的输出结果是 A 4 B 6 C 8 D 10
下列程序的输出结果是 A 5 B 6 C 7 D 8
语句printf("a\bre\'hi\'y\\\bou\n");的输出结果是 A a\bre\'hi\'y\\\bou B a\bre\'hi\'y\bou C re'hi'you D abre'hi'y\bou
设已有定义: char *st="how are you"; 下列程序段中正确的是
A) char a[11], *p; strcpy(p=a+1,&st[4]);
B) char a[11]; strcpy(++a, st);
C) char a[11]; strcpy(a, st);
D) char a[], *p; strcpy(p=&a[1],st+2);下列程序执行后的输出结果是 A) you&me 
you C) me D) err