#include <iostream>

using namespace std;/** 编写反转字符串的程序，要求优化速度、优化空间。*/void reverse(char *str,int len){char *p = str;char *q = str + len - 1;    len /= 2;while(len > 0)    {*p = *p ^ *q;*q = *p ^ *q;*p = *p ^ *q;        p ++;        q --;        len --;    }}int main(){char str[11] = "9876543210";    reverse(str,sizeof(str) - 1);

    cout << str << endl;return 0;}

#include <iostream>#include <stdio.h>#include <stdlib.h>using namespace std;struct node{int key;    node *next;};node * head;void create(){int i;    node *p = NULL;    head = (node *)malloc(sizeof(node));    head->key = 0;    head->next = NULL;

    p = head;

for(int i = 0;i < 6;i ++)    {        p->next = (node *)malloc(sizeof(node));        p->next->key = i;        p->next->next = NULL;        p = p->next;    }    p->next = head;//使尾节点指向头节点

    #ifdef TEST    p = head;for(int i = 0;i < 12;i ++)        cout << p->key << " ";    cout << endl;#endif

}

void test(){    node *p = NULL;    node *pp = NULL;    p = head->next;    pp = head->next->next;while(pp != p)    {        p = p->next;        pp = pp->next->next;if(p == NULL || pp == NULL)        {            cout << "不是循环链表" << endl;return ;        }    }    cout << "是循环链表" << endl;

}

void des(){    node *p = NULL,*q = NULL;    p = head->next;while(p != head)    {        q = p;        p = p->next;        free(q);    }    free(head);}int main(){    create();    test();    des();return 0;}

#include <iostream>#include <stdio.h>#include <string.h>using namespace::std;

const int MAX = 10;

int my_power(int n){if(n <= 0)return 1;int temp = 1;while (n--)temp *= 10;return temp;}

float convert(const char* str){float sum1 = 0.0;float sum2 = 0.0;int i = 0;int idx = 0;int len = strlen(str);

while(str[idx] != '.' && str[idx] != '\0')idx++;

while(i < idx){sum1 = sum1 * 10 + (str[i]-'0'); //整数部分i ++;}i = idx + 1;if(i < len){while(i < len){sum2 = sum2 * 10 + (str[i]-'0');i ++;}}

return (sum1+sum2/my_power(len - idx - 1));}int main(){float result = 0.0;char str[MAX];cin >> str;result = convert(str);cout << result << endl;return 0;}

#include <iostream>

using namespace std;

/*写一个函数，检查字符串是否是整数，如果是，返回其整数值。*/

long convert(const char * str){long value = 0,f = 1;if(* str == '-') str ++,f = -1;for(; *str != '\0' && *str >= '0' && *str <= '9'; str ++) value = value * 10 + (*str - '0');

return *str == '\0' ? value * f:0;}int main(){char str[] = "123456789";    cout << convert(str) << endl;

char str3[] = "-1234567";    cout << convert(str3) << endl;

return 0;}

#include <iostream>#include <iomanip>using namespace std;inline bool IsNum(const char c){return c >= '0' && c <= '9';}

inline bool IsAlpha(const char c){return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');}

// 从字符串str中获得一个浮点数// start表示这个浮点数在字符串中的起始位置。end表示浮点数结束的下一个位置// dot表示小数点所在的位置bool CheckString(const char* str, int& start, int& dot, int& end){if (str == NULL)//字符串为空        return false;

char* p = const_cast<char*>(str);

while(!IsNum(*p++));    p--;    start = p - str;

if (str[start - 1] == '.')// -.14f    {        start--; p--;    }

for (; IsNum(*p); p++);

if (*p == '.')    {        dot = p - str;while(IsNum(*++p));        end = p - str;return true;    }

    dot = p - str;    end = p - str;return true;}

//a^bdouble Pow(const int a, const int b){double rslt = 1;for (int i = 0; i < b; i++)        rslt *= a;

return rslt;}// 把一个字符串转化成double型的浮点数double Atof(const char* str){int s, d, e;if (!CheckString(str, s, d, e))    {        cout << "please check your string." <<endl;return 0;    }double result = 0.0;

double pow = Pow(10, e - 1 - d);

// 计算小数部分    for (int i = e - 1; i > d; i--)    {        result += (str[i] - '0') / pow;        pow /= 10;    }

    pow = 1;// 计算整数部分    for (int j = d - 1; j >= s; j--)    {        result += (str[j] - '0') * pow;        pow *= 10;    }

if (s > 0 && str[s - 1] == '-')        result = -result;

return result;}int main(){    cout << endl;    cout << endl  << setprecision(10) << Atof("-123.456") << endl;return 0;}