经典C程序

1、将一个链表逆序

LinkList *reverse(LinkList *head)
{
  LinkList *p1,*p2 = NULL,*p3 = NULL;
  if(head == NULL || head->next == NULL)
    return head;
  p1 = head->next;
  while(p1!=NULL)
  {
    p3 = p1->next;
    p1->next = p2;
    p2 = p1;
    p1 = p3;
 }
 head->next = p2;
  // head = p2;


  return head;
}

2、计算一个字节里（byte）里面有多少bit被置1 

#include <stdio.h>

int comb(const int c)
{
int count = 0;
int i = 0;
int cc = c;
while(i <8)
{
    if((cc&1)==1)
    {
        count ;
    }
    cc = cc>>1;
}
return count;
}

int main()
{
const int c = 0xcf;
printf("%d\n",comb(c));
return 1;
}

3、在一个字符串中找到可能的最长的子字符串

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char *commanstring(char shortstring[],char longstring[])
{
  int i,j;
  char *substring = malloc(256);
  if(strstr(longstring,shortstring)!=NULL)
    return shortstring;
  for(i=strlen(shortstring)-1;i>0;i--)
  {
    for(j=0;j<=strlen(shortstring)-i;j )
    {
      memcpy(substring,&shortstring[j],i);
    substring[i]='\0';
    if(strstr(longstring,substring)!=NULL)
      return substring;
    }
  }
  return NULL;
}

void main(void)
{
  char *str1 = "aocdfe";
  char *str2 = "pmcdfa";
  char *comman = NULL;
  if(strlen(str1)>strlen(str2))
    comman= commanstring(str2,str1);
  else
    comman = commanstring(str1,str2);
  printf("the longest comman string is:%s\n",comman);
  
 }

4、字符串转换为整数 

#include <stdio.h>
#include <string.h>
void reverse(char s[])
{ //字符串反转

    int c, i=0, j;
    for(j=strlen(s)-1;i<j;j--)
    { c=s[i];
        s[i]=s[j];
        s[j]=c;
        i ;
    }
}
void IntegerToString(char s[],int n)
{ int i=0,sign;
    if((sign=n)<0)//如果是负数，先转成正数

        n=-n;
    do //从个位开始变成字符,直到最高位,最后应该反转

    { s[i ]=n%10 '0';
    }while((n=n/10)>0);
    //如果是负数，补上负号

    if(sign<0)
        s[i ]='-';
    s[i]='\0';//字符串结束

    reverse(s);
}
void main()
{ int m;
    char c[100];
    m =215;
    IntegerToString(c,m);
    printf("integer = %d string = %s\n", m, c);
}

5、整数转换为字符串

#include <stdio.h>
#include <string.h>
int Atoi(char str[])
{
int i;
int weight = 1; // 权重

int rtn = 0; // 用作返回


for(i = strlen(str) - 1; i >= 0; i--)
{
   rtn = (str[i] - '0')* weight; //

   weight *= 10; // 增重

}

return rtn;
}

void main()
{
char str[32];

printf("Input a string :");
gets(str);

printf("%d\n", Atoi(str));
}

6、将一个字符串逆序

#include
#include
#include
#include
string_reverse(char *a)
{
        int i=0;
        char temp=0;
        char *ps;
        char *pe;
        if(a==NULL)
        return;
        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;
        }
}

int main()
{
        char *str;
        str=malloc(50);
        if(str==NULL)
                printf("error\n");
        else
                memcpy(str,"a123456789",11);
        printf("%s\n",str);
        string_reverse(str);
        printf("The new string is %s\n",str);
        free(str);
        return 0;
}