c实验5
实验任务1 #include<stdio.h> #define N 4 int main() { int x[N]={1,9,8,4}; int i; int *p; for(i=0;i<N;++i) printf("%d",x[i]); printf("\n"); for(p=x;p<x+N;++p) printf("%d",*p); printf("\n"); p=x; for(i=0;i<N;++i) printf("%d",*(p+i)); printf("\n"); p=x; for(i=0;i<N;++i) printf("%d",p[i]); printf("\n"); return 0; }
#include<stdio.h> int main() { int x[2][4]={{1,9,8,4},{2,0,4,9}}; int i,j; int *p; int(*q)[4]; for(i=0;i<2;++i) { for(j=0;j<4;++j) printf("%d",x[i][j]); printf("\n"); } for(p=&x[0][0],i=0;p<&x[0][0]+8;++p,++i) { printf("%d",*p); if((i+1)%4==0) printf("\n"); } for(q=x;q<x+2;++q) { for(j=0;j<4;++j) printf("%d",*(*q+j)); printf("\n"); } return 0; }
实验任务2 #include<stdio.h> #include<string.h> #define N 80 int main() { char s1[]="Learning makes me happy"; char s2[]="Learning makes me sleepy"; char tmp[N]; printf("sizeof(s1) vs.strlen(s1):\n"); printf("sizeof(s1)=%d\n",sizeof(s1)); printf("strlen(s1)=%d\n",strlen(s1)); printf("\nbefore swap:\n"); printf("s1:%s\n",s1); printf("s2:%s\n",s2); printf("\nswapping…\n"); strcpy(tmp,s1); strcpy(s1,s2); strcpy(s2,tmp); printf("\nafter swap:\n"); printf("s1:%s\n",s1); printf("s2:%s\n",s2); return 0; }
数组s1的大小是24。sizeof(s1)计算的是s1中所有的字符数。strlen(s1)统计的是s1中除了空字符以外的字符数。line7不能换成以下的写法，因为定义数组需要指出大小，而且不能把字符串直接赋值给数组。line20-22执行后，字符数组s1和s2中的内容交换了。
#include<stdio.h> #include<string.h> #define N 80 int main() { char *s1="Learning makes me happy"; char *s2="Learning makes me sleepy"; char *tmp; printf("sizeof(s1) vs.strlen(s1):\n"); printf("sizeof(s1)=%d\n",sizeof(s1)); printf("strlen(s1)=%d\n",strlen(s1)); printf("\nbefore swap:\n"); printf("s1:%s\n",s1); printf("s2:%s\n",s2); printf("\nswapping…\n"); tmp=s1; s1=s2; s2=tmp; printf("\nafter swap:\n"); printf("s1:%s\n",s1); printf("s2:%s\n",s2); return 0; }
指针变量s1中存放的是字符串"Learning makes me happy"的地址。sizeof(s1)计算的是字符串"Learning makes me happy"的地址的大小。strlen(s1)统计的是字符串"Learning makes me happy"中除了空字符以外的字符数。line7代码能替换成下面的写法，其含义是将常量字符串首地址赋值给字符指针。而task2_1.c中的line7是用字符串对字符数组初始化。line20-line22，交换的是指向字符串常量"Learning makes me happy"和字符串常 量"Learning makes me sleepy"的指针。字符串常量"Learning makes me happy"和字符串常 量"Learning makes me sleepy"在内存存储单元中没有交换。
实验任务3 #include<stdio.h> void str_cpy(char *target,const char *source); void str_cat(char *str1,char *str2); int main() { char s1[80],s2[20]="1984"; str_cpy(s1,s2); puts(s1); str_cat(s1," Animal Farm"); puts(s1); return 0; } void str_cpy(char *target,const char *source) { while(*target++=*source++) ; } void str_cat(char *str1,char *str2) { while(*str1) str1++; while(*str1++=*str2++) ; }
实验任务4 #include<stdio.h> #define N 80 int func(char *); int main() { char str[80]; while(gets(str)!=NULL) { if(func(str)) printf("yes\n"); else printf("no\n"); } return 0; } int func(char *str) { char *begin,*end; begin=end=str; while(*end) end++; end--; while(begin<end) { if(*begin!=*end) return 0; else { begin++; end--; } } return 1; }
实验任务5 #include<stdio.h> #define N 80 void func(char *); int main() { char s[N]; while(scanf("%s",s)!=EOF) { func(s); puts(s); } return 0; } void func(char *str) { int i; char *p1,*p2,*p; p1=str; while(*p1=='*') p1++; p2=str; while(*p2) p2++; p2--; while(*p2=='*') p2--; p=str; i=0; while(p<p1) { str[i]=*p; p++; i++; } while(p<=p2) { if(*p!='*') { str[i]=*p; i++; } p++; } while(*p!='\0') { str[i]=*p; p++; i++; } str[i]='\0'; }
实验任务6 #include<stdio.h> #include<string.h> void sort(char *name[],int n); int main() { char *course[4]={"C Program", "C++ Object Oriented Program", "Operating System", "Data Structure and Algorithms"}; int i; sort(course,4); for(i=0;i<4;i++) printf("%s\n",course[i]); return 0; } void sort(char *name[],int n) { int i,j; char *tmp; for(i=0;i<n-1;++i) for(j=0;j<n-1-i;++j) if(strcmp(name[j],name[j+1])>0) { tmp=name[j]; name[j]=name[j+1]; name[j+1]=tmp; } }
#include<stdio.h> #include<string.h> void sort(char *name[],int n); int main() { char *course[4]={"C Program", "C++ Object Oriented Program", "Operating System", "Data Structure and Algorithms"}; int i; sort(course,4); for(i=0;i<4;i++) printf("%s\n",course[i]); return 0; } void sort(char *name[],int n) { int i,j,k; char *tmp; for(i=0;i<n-1;i++) { k=i; for(j=i+1;j<n;j++) if(strcmp(name[j],name[k])<0) k=j; if(k!=i) { tmp=name[i]; name[i]=name[k]; name[k]=tmp; } } }
这两种算法实现中，交换的是指针变量的值。
实验任务7 #include<stdio.h> #include<string.h> #define N 5 int check_id(char *str); int main() { char *pid[N]={"31010120000721656X", "330106199609203301", "53010220051126571", "510104199211197977", "53010220051126133Y"}; int i; for(i=0;i<N;++i) if(check_id(pid[i])) printf("%s\tTrue\n",pid[i]); else printf("%s\tFalse\n",pid[i]); return 0; } int check_id(char *str) { if(strlen(str)!=18) return 0; else { char *p; p=str; while(*p>='0'&&*p<='9'&&*p!='\0'||*p=='X') p++; if(*p=='\0') return 1; else return 0; } }
实验任务8 #include<stdio.h> #define N 80 void encoder(char *s); void decoder(char *s); int main() { char words[N]; printf("输入英文文本："); gets(words); printf("编码后的英文文本："); encoder(words); printf("%s\n",words); printf("对编码后的英文文本解码："); decoder(words); printf("%s\n",words); return 0; } void encoder(char *s) { char *p; p=s; while(*p) { if(*p>='a'&&*p<='y'||*p>='A'&&*p<='Z') (*p)++; else if(*p=='z'||*p=='Z') *p=*p-25; p++; } } void decoder(char *s) { char *p; p=s; while(*p) { if(*p>='b'&&*p<='z'||*p>='B'&&*p<='Z') (*p)--; else if(*p=='A'||*p=='a') *p=*p+25; p++; } }
实验总结：本次实验中，我更加深入地理解了上课学的指向字符类型的指针变量和字符串的区别等内容，第一次实践了判断回文和选择排序。实验任务7和8是我第一次独立地进行指针的编程，让我意识到一种方法不行时就要改变方法，可以考虑指针指向的字符能不能达到'\0'.实验任务8表明，若while的条件是*p++,则不能加密第一个字符。
