《The C Programming Language》答案（第七章）

P1

/**Write a program that converts upper case to lower or lower case to upper, depending * on the name it is invoked with as found in argv[0]**/#include 
   
    #include 
    
     #include 
     
      void printc(int (*f)(int)){
       char c;    while ((c=getchar())!=EOF)        putchar(f(c));}int main(int argc,char* argv[]){
       if(strcmp(argv[0],"lower")==0)        printc(tolower);    if(strcmp(argv[0],"upper")==0)        printc(toupper);    return 0;}

P2

/** * write a program that will print arbitrary input in a sensible way. As a minimum, it * should print non graphic characters in octal or hexadecimal according to local custom, * and break long text lines. **/#include 
   
    #define LINELEN 14#define OCTLEN 3int printnor(int c,int n){
       int len;    if((len=(n+1))<=LINELEN)        printf("%c",c);    else        printf("\n%c",c);    return len;}int printoct(int c,int n){
       int len;    if((len=(n+OCTLEN))<=LINELEN)        printf("%o",c);    else        printf("\n%o",c);    return len;}int main(){
       int c,cnum = 0;    while((c=getchar())!=EOF){
           cnum=(c<32)?printoct(c,cnum):printnor(c,cnum);        if(cnum>=LINELEN)            cnum=cnum-LINELEN;    }    return 0;}

P3

/** * Revise miniprintf to handle more of the other  * facilities of printf **/#include 
   
    #include 
    
     void miniprintf(char* fmt,...){
       va_list ap;    char *p,*sval;    int ival;    double dval;    va_start(ap, fmt); // make ap point ot 1st unnamed arg    for (p = fmt; *p; p++){
         if (*p != '%'){
        putchar(*p);     continue; }      switch (*++p){
        case 'i':     case 'd':         ival = va_arg(ap, int);         printf("%d", ival);         break;     case 'o':         ival = va_arg(ap, int);         printf("%o", ival);         break;     case 'X':     case 'x':         ival = va_arg(ap, int);         printf("%x", ival);         break;     case 'u':         ival = va_arg(ap, int);         printf("%u", ival);         break;     case 'c':         ival = va_arg(ap, int);         printf("%c", ival);         break;     case 'G':     case 'g':        case 'E':     case 'e':     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}int main(){
       miniprintf("This is Spart%c!\n",'a');}

P4

/** * Write a private version of scanf analogous to  * miniprintf from the previous section **/#include 
   
    #include 
    
     void keep_reading(){
       char c;    while((c=getchar())!='\n'||c!=EOF)        ;}int mscanf(char* fmt,...){
       va_list ap;    char *p,*sval,c;    int ival,count=0;    double dval;    va_start(ap, fmt); // make ap point ot 1st unnamed arg    for (p = fmt; *p; p++){
           if (*p != '%'){
            c = getchar();         if (c != *p){
                keep_reading();             return 0;     }     else         continue; }    switch (*++p){
        case 'd':         ival = va_arg(ap, int);         count += scanf("%d", &ival);         break;     case 'f':         dval = va_arg(ap, double);         count += scanf("%lf", &dval);         break;     case 's':         sval = va_arg(ap, char *);         count += scanf("%s", sval);         break;     default:         printf("wrong format!");         return 0;     }    }    va_end(ap);    // clean up when done    return count;}int main(){
       int a;    scanf("-%d",&a);//-114514    printf("%d\n",a);//114514}

P5

/** * Rewrite the postfix calculator of Chapter 4 to * use scanf and/or sscanf to do the input and  * number conversion **/#include 
   
    #include 
    
     #define MAXLINE 114double atof(char s[]){
       double val,power;    int i,sign;    for(i=0;s[i]==' ';i++)        ;    sign = (s[i]=='-')?-1:1;    if((s[i]=='+')||(s[i]=='-'))        i++;    for(val=0.0;isdigit(s[i]);i++)        val=val*10.0+(s[i]-'0');    if(s[i]=='.')        i++;    for(power=1.0;isdigit(s[i]);i++){
           val=10.0*val+(s[i]-'0');        power*=10.0;    }    return (sign*val/power);}int main(){
       double sum,atof(char s[]);    char s[MAXLINE];    int x;    sum = 0;    while(scanf("%s",s)!=EOF)        printf("\t%g\n",sum+=atof(s));    return 0;}

P6

/** * Write a program to compare two files, printing the first * line where thet differ. **/#include 
   
    #include 
    
     #define MAXLINE 114int main(int argc,char* argv[]){
       FILE *f1, *f2;    char l1[MAXLINE], l2[MAXLINE];    char *prog = argv[0];    if (argc != 3){
           printf("error: the program takes 2 arguments;\n");        return 0;    }    else if ((f1 = fopen(*++argv, "r")) != NULL)             if ((f2 = fopen(*++argv, "r")) != NULL)             while (fgets(l1, MAXLINE, f1) != NULL && fgets(l2, MAXLINE, f2) != NULL){
                    if (strcmp(l1, l2) != 0){
                     printf("%s", l1);                  printf("%s", l2);                  fclose(f1);                  fclose(f2);                  return 0;                 }             }            else{
                fprintf(stderr, "%s can't open %s", prog, *argv);             exit(1);         }    else{
        fprintf(stderr, "%s can't open %s", prog, *argv);     exit(1);    }    printf("Identical lines\n");    return 0;}

P7

/** Modify the pattern finding program of Chapter 5 to take its input from a * set of named files or, if no files are named as arguments, form the standard * input. Should the file name be printed when a matching line is found? **/#include 
   
    #include 
    
     #define MAXLINE 1919#define PATTERNLEN 114int getline(char* s,int lim){
       int c,i;    i=0;    while(--lim>0&&(c==getchar())!=EOF&&c!='\n')        s[i++]=c;    if(c=='\n')        s[i++]=c;    s[i]='\0';    return i;}int main(int argc,char* argv[]){
       FILE *f;    char line[MAXLINE], *pattern;    long lineno = 0;    int c, except = 0, number = 0, found = 0;    int argn = 1;    while(++argn < argc && ((*++argv)[0] == '-'))        while (c = *++argv[0])            switch (c){
                case 'x':                 except = 1;                 break;             case 'n':                 number = 1;                 break;             default:                 printf("find: illegal option %c\n", c);                 argc = 0;                 found = -1;                 break;             }  if (argn++ <= argc){
           pattern = *argv;        if (argn <= argc){
            lineno = 0;         while(*++argv != NULL){
                printf("%s\n", *argv);             if ((f = fopen(*argv, "r")) != NULL){
                 while (fgets(line, MAXLINE, f) != NULL){
                     lineno++;                  if ((strstr(line, pattern) != NULL) != except){
                      if (number)                       printf("%ld:", lineno);               printf("%s", line);               found++;               }              }          }             else              printf("error: could not open %s", *argv);         }     }        else         while (getline(line, MAXLINE) > 0){
                lineno++;             if ((strstr(line, pattern) != NULL) != except){
                 if (number)                  printf("%ld:", lineno);              printf("%s", line);              found++;             }         }    }    else        printf("Usage: find -x -n pattern [textfile\\s]\n");    return found;}

P8

/** * Write a program to print a set of files, starting each * new one on a new page, with a title and a running page * count for each file. **/#include 
   
    #define MAXLINE 1919#define PAGEROWS 81int count_pages(FILE* f){
       int rows=0;    char line[MAXLINE];    while ((fgets(line,MAXLINE,f))!=NULL)        rows++;    rewind(f);    return rows/PAGEROWS+1;}int main(int argc,char* argv[]){
       FILE* f;    int pages = 0,rows,i;    char line[MAXLINE];    int count_pages(FILE *f);    if(argc==1){
           printf("Not enough parameters!\n");        return 0;    }    else        while (--argc > 0)            if ((f = fopen(*++argv, "r")) != NULL){
                pages = count_pages(f);             printf("File: %s, %d pages\n", *argv, pages);             rows = 0;             if ((fgets(line, MAXLINE, f)) == NULL)                 printf("NULL");             while ((fgets(line, MAXLINE, f)) != NULL){
                    rows++;                 printf("%s", line);             }             for (i = rows % PAGEROWS; i <= PAGEROWS; i++ )                 printf("\n");             fclose(f);         }            else{
                fprintf(stderr, "can't open file %s", *argv);             exit(1);         }  return 0;}

P9

/** * functions like isupper can be implemented to save space * or to save time. Explore both possibilities. **///二种形式#include 
   
    #include 
    
     #include 
     
      int isupper(int c){
       return (c>='A'&&c<='Z');}int isupper(int c){
       return (strchr("ABCDEFGHIJKLMNOPQRSTUVWXYZ",c)!=NULL);}