使用c语言实现的常用函数

/* 为了面试准备的，有些在工作中也可以用用，本人算法方面比较欠缺，如果有更优秀的算法麻烦告诉我啊 */

/* strcat的实现 */

#include <assert.h>

char* my_strcat (char* strDest,const char* strSrc)

{

char *ret = strDest;

assert ((strDest != NULL)  &&  (strSrc != NULL));

while (*strDest != '\0')

{

strDest++;

}

while ((*strDest++ = *strSrc++) != '\0')

{

}

*strDest = '\0';

return ret;

}

/* strcpy的实现 */

#include <assert.h>

char* my_strcpy (char* strDest, const char* strSrc)

{

assert ((strDest != NULL) && (strSrc != NULL));

char* address = strDest;

while ((*strDest++ = *strSrc++) != '\0')

{

}

return address;

}

/* split的实现 */

int my_split (char *strOld, char **strNew)

{

assert ((strOld != NULL) && (strNew != NULL));

char *emp = *strNew;

int res = 0;

for (;;)

{

if ((*strOld >= '0') && (*strNew <= '9'))

{

int j = *strOld - '0';

res = res * 10 + j;

strOld++;

}

else if ((*strOld >= 'A') && (*strOld <= 'z'))

{

*emp++ = *strOld;

strOld++;

}

else

{

break;

}

}

return res;

}

/* strcmp的实现 */

int my_strcmp (const char *strDest, const char* strSrc)

{

while (*strDest)

{

if (*strDest != *strSrc)

{

return (*strDest - *strSrc) > 0 ? 1 : -1;

}

strDest++;

strSrc++;

}

if (*strDest)

{

return -1;

}

else

{

return 0;

}

}

/* string 转换为int */

int my_atoi (const char *str)

{

int result = 0;

int sign = 1;

if ('0' <= str[0] && str[0] <= '9' || (str[0] == '-') || (str[0] == '+'))

{

if (str[0] == '+' || str[0] == '-')

{

if (str[0] == '-')

{

sign = -1;

}

else

{

str++;

}

}

}

while (*str>='0' && *str<='9')

{

result = result * 10 + (*str - '0');

str++;

}

return result * sign;

}

/* int 转换为16进制 */

void my_itoa (char *buffer, unsigned int num)

{

int i;

unsigned int tmp;

buffer[0] = '0';

buffer[1] = 'x';

i = 9;

while (num)

{

tmp = num % 16;

if (tmp >= 10)

{

buffer[i] = tmp - 10 + 'A';

}

else

{

buffer[i] = tmp + '0';

}

i--;

num /= 16;

}

while (i >= 2)

{

buffer[i--] = '0';

}

buffer[10] = 0;

}

/* 字符串逆序 */

int str_reversed(char *str)

{

int i = 0;

char temp = 0;

char *ps;

char *pe;

if (!str)

{

return -1;

}

ps = a;

while (*a != 0)

{

a++;

}

pe = a;

for (i=0; i<(pe-ps)/2;i++)

{

temp = *(ps+i);

*(ps+i) = *(pe-i-1);

*(pe-i-1) = temp;

}

return 0;

}

/* 冒泡排序 */

void bubble_sort (int arr[], int size)

{

int i,j,flag,temp;

for (i=1; i<=size-1; i++)

{

flag = 0;

for (j=0; j<=size-i-1; j++)

{

if (arr[j] > arr[j+1])

{

flag = 1;

temp = arr[i];

arr[i] = arr[i+1];

arr[i+1] = temp;

}

if (flag == 0)

{

break;

}

}

}

}

/* 链表逆序*/

list reverse_list (list n)

{

if (!n)

{

return n;

}

list cur = n.next;

list pre = n;

list tmp;

pre.next = NULL;

while (NULL != cur.next)

{

tmp = cur;

tmp.next = pre;

pre = tmp;

cur = cur.next;

}

return tmp;

}

/* 判断是否是质数（素数） */

int is_prime (int n)

{

int i;

if (n < 2) return 0;

if (n == 2) return 1;

//判断时只需判断到n的开方即可

for (i=2; i*i<=n; i++)

{

if (n%i == 0) return 0;

}

return 1;

}

//打印小于num的所有素数

void print_prime (int num)

{

int i = 2;

if (num >= 2)

{

printf ("%d",i);

}

//去除偶数

for (i=3; i<num; i+=2)

{

if (is_prime(i))

{

printf ("%d",i);

}

}

}

/* 递归题 */

//阶乘

int mul (int num)

{

if (num == 1) return 1;

return num*mul(num-1);

}

//斐波那契数列

int fei (int num)

{

if (num==0 || num==1) return num;

return f(num-1) + f(num-2);

}

/* 全局变量模拟栈操作 */

#include <stdio.h>

#include <stdbool.h>

int INDEX;

int data[20];

//入栈

bool push(int d)

{

if (INDEX >= 20)return false;

data[INDEX++] = d;

return true;

}

//出栈

int pop()

{

return data[--INDEX];

}

//返回栈顶

int peak()

{

return data[INDEX-1];

}

//判断栈是否空

bool empty()

{

if (INDEX <= 0) return true;

return false;

}