《The C Programming Language》答案（第二章）

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P1

#include 
   
    #include 
    
     //肖战,nmslint main(){
       printf("Domain of signed char is [%d, %d].\n",SCHAR_MIN,SCHAR_MAX);    printf("Domain of unsigned char is [%u, %u].\n",0,UCHAR_MAX);    printf("Domain of char is [%d, %d].\n",CHAR_MIN,CHAR_MAX);    printf("Domain of signed short int is [%hd, %hd].\n",SHRT_MIN,SHRT_MAX);    printf("Domain of unsigned short int is [%hu, %hu].\n",0,USHRT_MAX);    printf("Domain of signed int is [%d, %d].\n",INT_MIN,INT_MAX);    printf("Domain of unsigned int is [%u, %u].\n",0,UINT_MAX);    printf("Domain of signed long int is [%ld, %ld].\n",LONG_MIN,LONG_MAX);    printf("Domain of unsigned long int is [%lu, %lu].\n",0,ULLONG_MAX);    return 0;}

P2

#include 
   
    #define MAXLINE 1024int main(){
       char line[MAXLINE];    int c,i;    i=0;    while(i

P3

#include 
   
    #define MAXLINE 1024int get_line(char s[],int lim){
       int c,i,l;    for(i=0,l=0;(c=getchar())!=EOF&&c!='\n';++i)        if(i
    
     ='0'&&c<='9')            n+=c-'0';        else if(c>='a'&&c<='f')            n+=c-'a';        else if(c>='A'&&c<='F')            n+=c-'A';    }    return n;}int main(){
       int len;    char line[MAXLINE];    while((len=get_line(line,MAXLINE))>0)        printf("%lu\n",htoi(line));    return 0;}

P4

#include 
   
    #define MAXLINE 1024int get_line(char line[], int maxline);void squeeze(char s1[], char s2[]);int main(void){
       int len;    char s1[MAXLINE];    char s2[MAXLINE];    printf("Input string s1:\n");    while ((len = get_line(s1, MAXLINE)) == 0)        ;    printf("Input string s2:\n");    while ((len = get_line(s2, MAXLINE)) == 0)        ;    squeeze(s1, s2);    printf("Result is %s\n", s1);    return 0;}int get_line(char s[], int lim){
       int c, i, l;    for (i = 0, l = 0; (c = getchar()) != EOF && c != '\n'; ++i)        if (i < lim - 1)            s[l++] = c;    s[l] = '\0';    return l;}void squeeze(char s1[], char s2[]){
       int i=0;//s1 ptr    char tmp[MAXLINE];    int k=0;//tmp ptr    while(s1[i]!='\0'){
           int find_flag = 0;        int j=0;//s2 ptr        while(s2[j]!='\0'){
               if(s1[i]==s2[j]){
   //match!                find_flag=1;                break;            }            j++;        }        if(find_flag==0){
               tmp[k]=s1[i];            k++;        }        i++;    }    tmp[k]='\0';    for(int ii=0;ii

P5

#include 
   
    #define MAXLINE 1024int get_line(char line[], int maxline);void squeeze(char s1[], char s2[]);int main(void){
       int len;    char s1[MAXLINE];    char s2[MAXLINE];    printf("Input string s1:\n");    while ((len = get_line(s1, MAXLINE)) == 0)        ;    printf("Input string s2:\n");    while ((len = get_line(s2, MAXLINE)) == 0)        ;    squeeze(s1, s2);    printf("Result is %s\n", s1);    return 0;}int get_line(char s[], int lim){
       int c, i, l;    for (i = 0, l = 0; (c = getchar()) != EOF && c != '\n'; ++i)        if (i < lim - 1)            s[l++] = c;    s[l] = '\0';    return l;}int any(char s1[], char s2[]){
       int i, j;    i = 0;    while (s2[i] != '\0') {
           j = 0;        while (s1[j] != '\0') {
               if (s1[j] == s2[i])                return j;            ++j;        }        ++i;    }    return -1;}

P6

#include 
   
    unsigned setbits(unsigned x,int p,int n,unsigned y){
       unsigned maskA = x&~(~(~0U<
    
     <<(p+1-n));    unsigned maskB = (y&~(~0U<
     
      <<(p+1-n);    return maskA|maskB;}int main(){
       printf("%u\n",setbits(114514,1,9,19810));    return 0;}

P7

#include 
   
    unsigned invert(unsigned x,int p,int n){
       unsigned mask = ~(~0U<
    
     <<(p+1-n);    return x^mask;}int main(){
       printf("%u\n",invert(1145,19,14));    return 0;}

P8

#include 
   
    unsigned rightrot(unsigned x,int n){
       while(n-- >0)        if(x&1)            x = (x>>1)|~(~0U>>1);        else            x = x>>1;    return x;}int main(){
       printf("%u\n",rightrot(1145,1));    return 0;}

P9

原理：x-1在二进制上相当于把最右边为1的位置零，然后把这一位之后的所有位置1

#include 
   
    int bitcount(unsigned x){
       int bits;    for(bits=0;x!=0;x&=(x-1))        bits++;    return bits;}int main(){
       printf("%d\n",bitcount(114514));    return 0;}

P10

#include 
   
    int lower(int c){
       return (c>='A'&&c<='Z')?c+'a'-'A':c;}int main(){
       char jj[] = "YESHOUXIANBEI";    int i = 0;    while(jj[i]!='\0'){
           printf("%c--->%c\n",jj[i],lower(jj[i]));        i++;    }    return 0;}