编程练习4.25

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1. 统计一个字符串中个字符的百分比：如输入字符串asdfs a ----- 20%s ----- 40%d -----20%f -----20%

/*统计一个字符中个字符的百分比，如输入字符串asdfs，a--20% s--40%,d--20%,f--20%*/#include <stdio.h>#include <string.h>void fun(char *str,int a[]){int len = strlen(str);                                  //记录字符串的长度int i = 0;  char buffer[26];                                        //记录字符for(i = 0;i < 26;i++)                                   //将每个单词的个数按顺序存放在a数组中{if(str[i] >= 'a'&&str[i] <= 'z'){a[str[i]-'a']++;buffer[str[i]-'a'] = str[i];}}for(i = 0;i < 26;i++){if(a[i] == 0){continue;}else{printf("%c----%d%\n",buffer[i],a[i]*100/len);}}}int main(){char str[100] = {0};int a[26] = {0};printf("please input string:\n");scanf("%s",str);fun(str,a);return 0;}

,给一个字符串，有大小写字母，要求写一个函数把小写字母放在前面，大写字母放在后面，尽量使用最小空间，时间复杂度。（即用指针做）。

如：aAbBcCdD ---àabcdABCD

/*给一个字符串，有大小写字母，要求写一个函数把小写字母放在前面，大写字母放在后面，尽量使用最小的时间复杂度（即用指针做）如aAbBcCdD--->abcdABCD*/#include <stdio.h>#include <string.h>void my_move(char *str,char *result){int len = strlen(str);while(*str){if(*str >= 'a'&&*str <= 'z'){*result = *str;result++;}str++;}str = str-len;                                                //指针重新指向首地址while(*str){if(*str >= 'A'&&*str <= 'Z'){*result = *str;result++;}str++;}*result = '\0';}int main(){char str[100] = {0};char result[100] = {0};                                        //存放结果printf("please input string:\n");scanf("%s",str);my_move(str,result);printf("the result is:%s\n",result);return 0;}

3,自我实现atoi(字符串转整形)

如：“123”转换成 123

“-123” 转换成 -123

/*自我实现atoi字符串转整形 “－123”转为－123*/#include <stdio.h>int my_atoi(char *str){int temp = 0;int flag = 1;if(*str == '-')                                //判断是否是否为负数{flag = -1;str++;}else{flag = 1;}while(*str){temp =temp*10 + (*str-'0');str++;}return flag*temp;}int main(){char str[100] = {0};int temp = 0;printf("please input str:\n");scanf("%s",str);temp = my_atoi(str);printf("the result is:%d\n",temp);}

4，自我实现itoa(整形转字符串)

如： 123 转换成 “123”

“-123” 转换成-123

/*自我实现整形转字符串 例如－123转为“－123”*/#include <stdio.h>#include <string.h>void my_itoa(int m,char *str){char temp;int count = 0;                                  //记录字符串的长度int i = 0;if(m < 0)                                       //当第一个字符为负数的情况{*str = '-';str++;while(-m){*str = (-m)%10+'0';str++;count++;m = m/10;}*str = '\0';str = str-count-1;for(i = 1;i < (count+1)/2;i++)              //将字符串除了第一个，其他的逆序{temp = str[i];str[i] = str[count-i+1];str[count-i+1] = temp;}}else{while(m){*str = m%10+'0';str++;count++;m = m/10;}*str = '\0';str = str - count;for(i = 0;i < count/2;i++){temp = str[i];str[i] = str[count-i-1];str[count-i-1] = temp;}}}int main(){int num = 0;char str[100] = {0};char result[100] = {0};printf("please input the number:\n");scanf("%d",&num);my_itoa(num,str);printf("the result is :%s\n",str);}

5、统计字符串中子串的个数。

/*输入一个字符串，计算字符串中字串中子串出现的次数*/#include <stdio.h>#include <string.h>int fun(char *src,char *b)                     //b为定义的子串，src为主串{int count = 0;                             //记录子串的个数char *ptr = src;char *tt = b;                              int k = 0;                                 //记录相同字符的个数int len = strlen(b);while(*ptr != '\0'){while(*ptr == *tt&&*tt != '\0'){ptr++;tt++;k++;if(k == len)                       //长度为len时，计数器＋1{count++;k = 0;ptr--;}}tt = b;ptr++;}return count;}int main(){char src[100];char src_son[50];int count;printf("please input string1:\n");scanf("%s",src);printf("please input string_son:\n");scanf("%s",src_son);count = fun(src,src_son);printf("the result:%d\n",count);return 0;}

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