C语言练习5

返回“高级语言程序设计课程”目录

典型程序

输入行排序

   #include <stdio.h>
   #include <string.h>

   #define MAXLINES 5000     /* max #lines to be sorted */

   char *lineptr[MAXLINES];  /* pointers to text lines */

   int readlines(char *lineptr[], int nlines);
   void writelines(char *lineptr[], int nlines);

   void qsort(char *lineptr[], int left, int right);

   /* sort input lines */
   main()
   {
       int nlines;     /* number of input lines read */

       if ((nlines = readlines(lineptr, MAXLINES)) >= 0) {
           qsort(lineptr, 0, nlines-1);
           writelines(lineptr, nlines);
           return 0;
       } else {
           printf("error: input too big to sort\n");
           return 1;
       }
   }

   #define MAXLEN 1000  /* max length of any input line */
   int getline(char *, int);
   char *alloc(int);

   /* readlines:  read input lines */
   int readlines(char *lineptr[], int maxlines)
   {
       int len, nlines;
       char *p, line[MAXLEN];

       nlines = 0;
       while ((len = getline(line, MAXLEN)) > 0)
           if (nlines >= maxlines || p = alloc(len) == NULL)
               return -1;
           else {
               line[len-1] = '\0';  /* delete newline */
               strcpy(p, line);
               lineptr[nlines++] = p;
           }
       return nlines;
   }

   /* writelines:  write output lines */
   void writelines(char *lineptr[], int nlines)
   {
       int i;

       for (i = 0; i < nlines; i++)
           printf("%s\n", lineptr[i]);
   }
   /* qsort:  sort v[left]...v[right] into increasing order */
   void qsort(char *v[], int left, int right)
   {
       int i, last;
       void swap(char *v[], int i, int j);

       if (left >= right)  /* do nothing if array contains */
           return;         /* fewer than two elements */
       swap(v, left, (left + right)/2);
       last = left;
       for (i = left+1; i <= right; i++)
           if (strcmp(v[i], v[left]) < 0)
               swap(v, ++last, i);
       swap(v, left, last);
       qsort(v, left, last-1);
       qsort(v, last+1, right);
   }
   /* swap:  interchange v[i] and v[j] */
   void swap(char *v[], int i, int j)
   {
       char *temp;

       temp = v[i];
       v[i] = v[j];
       v[j] = temp;
   }

命令行参数指定查找字符串

   #include <stdio.h>
   #include <string.h>
   #define MAXLINE 1000

   int getline(char *line, int max);

   /* find:  print lines that match pattern from 1st arg */
   main(int argc, char *argv[])
   {
       char line[MAXLINE];
       int found = 0;

       if (argc != 2)
           printf("Usage: find pattern\n");
       else
           while (getline(line, MAXLINE) > 0)
               if (strstr(line, argv[1]) != NULL) {
                   printf("%s", line);
                   found++;
               }
       return found;
   }

函数指针

   #include <stdio.h>
   #include <string.h>

   #define MAXLINES 5000     /* max #lines to be sorted */
   char *lineptr[MAXLINES];  /* pointers to text lines */

   int readlines(char *lineptr[], int nlines);
   void writelines(char *lineptr[], int nlines);

   void qsort(void *lineptr[], int left, int right,
              int (*comp)(void *, void *));
   int numcmp(char *, char *);

   /* sort input lines */
   main(int argc, char *argv[])
   {
       int nlines;        /* number of input lines read */
       int numeric = 0;   /* 1 if numeric sort */

       if (argc > 1 && strcmp(argv[1], "-n") == 0)
           numeric = 1;
       if ((nlines = readlines(lineptr, MAXLINES)) >= 0) {
           qsort((void**) lineptr, 0, nlines-1,
             (int (*)(void*,void*))(numeric ? numcmp : strcmp));
           writelines(lineptr, nlines);
           return 0;
       } else {
           printf("input too big to sort\n");
           return 1;
       }
   }

   /* qsort:  sort v[left]...v[right] into increasing order */
   void qsort(void *v[], int left, int right,
              int (*comp)(void *, void *))
   {
       int i, last;

       void swap(void *v[], int, int);

       if (left >= right)    /* do  nothing if array contains */
           return;           /* fewer than two elements */
       swap(v, left, (left + right)/2);
       last = left;
       for (i = left+1; i <= right;  i++)
           if ((*comp)(v[i], v[left]) < 0)
               swap(v, ++last, i);
       swap(v, left, last);
       qsort(v, left, last-1, comp);
       qsort(v, last+1, right, comp);
   }

   #include <stdlib.h>

   /* numcmp:  compare s1 and s2 numerically */
   int numcmp(char *s1, char *s2)
   {
       double v1, v2;

       v1 = atof(s1);
       v2 = atof(s2);
       if (v1 < v2)
           return -1;
       else if (v1 > v2)
           return 1;
       else
           return 0;
   ｝

关键字统计

   #include <stdio.h>
   #include <ctype.h>
   #include <string.h>

   #define MAXWORD 100

   struct key {
       char *word;
       int count;
   } keytab[] = {
       "auto", 0,
       "break", 0,
       "case", 0,
       "char", 0,
       "const", 0,
       "continue", 0,
       "default", 0,
       /* ... */
       "unsigned", 0,
       "void", 0,
       "volatile", 0,
       "while", 0
   };


   int getword(char *, int);
   int binsearch(char *, struct key *, int);

   /* count C keywords */
   main()
   {
       int n;
       char word[MAXWORD];

       while (getword(word, MAXWORD) != EOF)
           if (isalpha(word[0]))
               if ((n = binsearch(word, keytab, NKEYS)) >= 0)
                   keytab[n].count++;
       for (n = 0; n < NKEYS; n++)
           if (keytab[n].count > 0)
               printf("%4d %s\n",
                   keytab[n].count, keytab[n].word);
       return 0;
   }

   /* binsearch:  find word in tab[0]...tab[n-1] */
   int binsearch(char *word, struct key tab[], int n)
   {
       int cond;
       int low, high, mid;

       low = 0;
       high = n - 1;
       while (low <= high) {
           mid = (low+high) / 2;
           if ((cond = strcmp(word, tab[mid].word)) < 0)
               high = mid - 1;
           else if (cond > 0)
               low = mid + 1;
           else
               return mid;
       }
       return -1;
   }
   /* getword:  get next word or character from input */
   int getword(char *word, int lim)
   {
       int c, getch(void);
       void ungetch(int);
       char *w = word;

       while (isspace(c = getch()))
           ;
       if (c != EOF)
           *w++ = c;
       if (!isalpha(c)) {
           *w = '\0';
           return c;
       }
       for ( ; --lim > 0; w++)
           if (!isalnum(*w = getch())) {
               ungetch(*w);
               break;
           }
       *w = '\0';
       return word[0];
   }

关键字统计指针版

   #include <stdio.h>
   #include <ctype.h>
   #include <string.h>
   #define MAXWORD 100

   int getword(char *, int);
   struct key *binsearch(char *, struct key *, int);

   /* count C keywords; pointer version */
   main()
   {
       char word[MAXWORD];
       struct key *p;

       while (getword(word, MAXWORD) != EOF)
           if (isalpha(word[0]))
               if ((p=binsearch(word, keytab, NKEYS)) != NULL)
                   p->count++;
       for (p = keytab; p < keytab + NKEYS; p++)
           if (p->count > 0)
               printf("%4d %s\n", p->count, p->word);
       return 0;
   }

   /* binsearch: find word in tab[0]...tab[n-1] */
   struct key *binsearch(char *word, struck key *tab, int n)
   {
       int cond;
       struct key *low = &tab[0];
       struct key *high = &tab[n];
       struct key *mid;

       while (low < high) {
           mid = low + (high-low) / 2;
           if ((cond = strcmp(word, mid->word)) < 0)
               high = mid;
           else if (cond > 0)
               low = mid + 1;
           else
               return mid;
       }
       return NULL;
   }

单链表自引用结构体

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAXWORD 1000
struct node {
    char *word;
    int count;
    struct node *next;
};

struct node*addlist(struct node *head, char *w);
char *strdup(char *s);
void listprint(struct node *p);

main() {
    struct node *head = NULL;
    char word[MAXWORD];
    while(getword(word, MAXWORD)!=EOF)
        if(isalpha(word[0]))
            head = addlist(head, word);
    listprint(head);
    system("pause");
}

void listprint(struct node *p) {
    while(p!=NULL) {
        printf("%4d %s\n", p->count, p->word);
        p = p->next;
    }
}

struct node*addlist(struct node *head, char *w){
    int cond;
    struct node *p = head, *pre = NULL;
    while(p!=NULL) {
        cond=strcmp(w,p->word);
        if(cond == 0) {
            p->count ++;
            return head;
        } else if(cond > 0) {
            pre = p; p = p->next;
        } else
            break;
    }
    p =(struct node*)malloc(sizeof(struct node));
    p->word = strdup(w);
    p->count = 1;
    if(pre == NULL) {
        p->next = NULL;
        head = p;
    } else {
        p->next = pre->next;
        pre->next = p;
    }
    return head;
}

char *strdup(char *s) {
    char *p = (char *)malloc(strlen(s)+1);
    strcpy(p, s);
    return p;
}


#define BUFSIZE 100
char buf[BUFSIZE]; /* buffer for ungetch */
int bufp = 0; /* next free position in buf */
int getch(void) /* get a (possibly pushed-back) character */
{
    return (bufp > 0) ? buf[--bufp] : getchar();
}

void ungetch(int c) /* push character back on input */ {
    if (bufp >= BUFSIZE)
        printf("ungetch: too many characters\n");
    else
        buf[bufp++] = c;
}

int getword(char *word, int lim)
{
    int c;
    char *w = word;

    while (isspace(c = getch()))
        ;
    if (c != EOF)
        *w++ = c;
    if (!isalpha(c)) {
        *w = '\0';
        return c;
    }
    for ( ; --lim > 0; w++)
        if (!isalnum(*w = getch())) {
            ungetch(*w);
            break;
        }
    *w = '\0';
    return word[0];
}

变长参数列表

   #include <stdarg.h>

   /* minprintf: minimal printf with variable argument list */
   void minprintf(char *fmt, ...)
   {
       va_list ap; /* points to each unnamed arg in turn */
       char *p, *sval;
       int ival;
       double dval;

       va_start(ap, fmt); /* make ap point to 1st unnamed arg */
       for (p = fmt; *p; p++) {
           if (*p != '%') {
               putchar(*p);
               continue;
           }
           switch (*++p) {
           case 'd':
               ival = va_arg(ap, int);
               printf("%d", ival);
               break;
           case 'f':
               dval = va_arg(ap, double);
               printf("%f", dval);
               break;
           case 's':
               for (sval = va_arg(ap, char *); *sval; sval++)
                   putchar(*sval);
               break;
           default:
               putchar(*p);
               break;
           }
       }
       va_end(ap); /* clean up when done */
   }

文件访问

   #include <stdio.h>

   /* cat:  concatenate files, version 1 */
   main(int argc, char *argv[])
   {
       FILE *fp;
       void filecopy(FILE *, FILE *)

       if (argc == 1) /* no args; copy standard input */
           filecopy(stdin, stdout);
       else
          while(--argc > 0)
              if ((fp = fopen(*++argv, "r")) == NULL) {
                  printf("cat: can't open %s\n, *argv);
                  return 1;
              } else {
                 filecopy(fp, stdout);
                 fclose(fp);
              }
          return 0;
   }

    /* filecopy:  copy file ifp to file ofp */
    void filecopy(FILE *ifp, FILE *ofp)
    {
        int c;

        while ((c = getc(ifp)) != EOF)
            putc(c, ofp);
    }

选择题

下列程序执行后的输出结果是 A 6 B 7 C 8 D 9

void func(int *a,int b[]) {
    b[0]=*a+6;
}
main() {
    int a,b[5];
    a=0;
    b[0]=3;
    func(&a,b);
    printf("%d\n,b[0]);
}

下列程序的输出结果是 A 4 B 6 C 8 D 10

int b=2;
int func(int *a) {
    b += *a;
    return b;
}
main() {
    int a=2, res=2;
    res += func(&a);
    printf("%d\n",res);
}

下列程序的输出结果是 A 5 B 6 C 7 D 8

struct abc {
    int a, b, c;
};
main() {
    struct abc  s[2]={{1,2,3},{4,5,6}};
    int t;
    t=s[0],a+s[1],b;
    printf("%d\n",t);
}

语句printf(“a'hi'y\”);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 B you C me D err

main() {
    char  arr[2][4];
    strcpy(arr[0],"you");
    strcpy(arr[1],"me");
    arr[0][3]='&';
    printf("%s\n",arr[0]);
}

假定下列程序的可执行文件名为prg.exe,则在该程序所在的子目录下输入命令行: prg hello good<回车>后,程序的输出结果是

  A) hello good   B) hg             C) hel           D) hellogood

main()(int argc, char *argv[]) {
    int  i;
    if(argc<1)
        return;
    for(i=1;i<argc;i++)
        printf("%c", *argv[i]);
}

以下函数返回a所指数组中最小的值所在的下标值

fun(int   *a,  int  n){
    int   i,j=0,p;
    p=j;
    for(i=j;i<n;i++)
        if(a[i]<a[p])
            __________;
    return p;
}

在下划线处应填入的是

A) i=p             B) a[p]=a[i]       C) p=j            D) p=i

若有以下的定义：int t[3][2];能正确表示t数组元素地址的表达式是

A) &t[3][2]        B) t[3]            C) t[1]           D) t[2]

有如下定义

struct person{
    char  name[9];
    int age;
};
struct person   p[10]={
 "Johu",  17,
 "Paul",  19,
 "Mary",  18,
 "Adam",  16
};

根据上述定义，能输出字母M的语句是

A) printf("%c\n",p[3].name);
B) pfintf("%c\n",p[3].name[1]);
C) prinft("%c\n",p[2].name[1]);
D) printf("%c\n",p[2].name[0]);

以下对结构体类型变量的定义中，不正确的是

A) typedef struct aa
{
   int   n;
   float m;
}AA;
AA td1;

B) #define AA    struct aa
AA {
   int n;
   float m;
}td1;

C) struct
{
   int n;
   float m;
}aa;
stuct aa td1;

D) struct
{
   int n;
   float m;
}td1;

有如下程序

main()
{
    char s[]="ABCD", *P;
    for(p=s+l; p<s+4; p++)
        printf ("%s\n", p);
}

该程序的输出结果是

A) ABCD            B) A               C) B              D) BCD
   BCD                B                  C                 CD
   CD                 C                  D                 D
   D                  D

有如下程序

main()
{
   char ch[2][5]={"6937","8254"},*p[2];
   int i,j,s=0;
   for(i=0;i<2;i++)
      p[i]=ch[i];
   for(i=0;i<2;i++)
      for(j=0;p[i][j]>'\0';j+=2)
         s=10*s+p[i][j]- '0';
   printf('%d\n',s);
}

该程序的输出结果是

A) 69825           B) 63825           C) 6385           D) 693825

函数pi的功能是根据以下近似公式求π值：

(π*π)/6=1+1/(2*2)+1/(3*3)+..+1/(n*n)

。现在请你在下面的函数中填空，完成求π的功能

#include <math.h>
double pi(long n) {
   double s=0.0;
   long i;
   for(i=1;i<=n;i++)
      s=s+_____________ ;
   return sqrt(6*s);
}

下列程序段的输出结果是

A) 2 1 4 3          B) 1 2 1 2          C) 1 2 3 4           D) 2 1 1 2

void fun(int  *x, int  *y){
    printf("%d  %d", *x, *y);
    *x=3;
    *y=4;
}
main(){
   int  x=1,y=2;
   fun(&y,&x);
   printf("%d %d",x, y);
}

下面程序把从终端读入的文本（用@作为文本结束标志）输出到一个名为bi.dat的新文件中。请填空。

#include <stdio.h>
main() {
   FILE  *fp;
   char  ch;
   if( (fp=fopen (_______________) ) == NULL)
      exit(0);
   while( (ch=getchar( )) !='@')
      putc (ch, fp);
   fclose(fp);
}

以下各选项说明一种新的类型名，其中正确的是

A) typedef  v1  int;            B) typedef  v2=int;
C) typedef  int  v3;        D) typedef  v4:  int;

以下程序的输出结果是

main(){
   char  st[20]= "hello\0\t\\\";
   printf("%d%d\n",strlen(st),sizeof(st));
}

A) 9 9          B) 5 20         C) 13 20        D) 20 20

以下选项中，不能正确赋值的是

A) char  s1[10]; s1="Ctest";
B) char  s2[]={'C', 't', 'e', 's', 't'};
C) char  s3[20]="Ctest";
D) char  *s4="Ctest";

若有定义：int aa[8];。则以下表达式中不能代表数组元aa[1]的地址的是

A) &aa[0]+1    B) &aa[1]       C) &aa[0]++      D) aa+1

以下程序的输出结果是

union myun
{
   struct{   int  x, y, z; } u;
   int  k;
} a;
main(){
   a.u.x=4; a.u.y=5; a.u.z=6;
   a.k=0;
   printf(%d\n”,a.u.x);
}

A) 4            B) 5            C) 6            D) 0

下面的程序执行后，文件test中的内容是

#include   <stdio.h>
void fun(char   *fname.,char   *st) {
    FILE  *myf;
    int   i;
    myf = fopen(fname,"w");
    for(i=0; i<strlen(st); i++)
        putc(st[i], myf);
    fclose(myf);
}
main()
{
   fun("test", "new world");
   fun("test","hello,");

A）hello，        B）new worldhello，   C）new world         D） hello, rld