C基础（46——50）

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#include <stdio.h>#include <stdlib.h>#include <assert.h>#include <math.h>double AtoF(char * str){                 assert(str );                 float num1=0;                 float num2=0;                 if(*str >='0' && * str<='9' )  //确保第一个字符必须是数字                {                                 while(*str !='.' && * str>='0' && *str<= '9')  //处理小数点前面的                                {                                                num1=num1*10+* str-'0' ;                                                 str++;                                }                                                                 if(*str =='.')                                                 str++;                                 //处理第一个小数点后面的                                 int i=1;                                 while(*str !='\0' && * str>='0' && *str<= '9')                                {                                                num2=num2+(* str-'0' )*(pow(0.1,i));                                                 str++;                                                i++;                                }                                 //已经走到字符串末尾                                 if(*str =='\0')                                                 return num1+num2;                                 else                                                 return 0;;                }                 else                                 return 0;}void test(){                 char* s1="12.34" ;                 char* s2="1234" ;                 char* s3="12.*34" ;  //异常                 char* s4="12.34.21" ;  //异常                 char* s5="12%34" ;  //异常                 char* s6="&12.34" ;  //异常                printf( "%f\n",AtoF(s1));                printf( "%f\n",AtoF(s2));                printf( "%f\n",AtoF(s3));                printf( "%f\n",AtoF(s4));                printf( "%f\n",AtoF(s5));                printf( "%f\n",AtoF(s6));}int main(){                test();                system( "pause");                 return 0;}

结果：

#include <stdio.h>#include <stdlib.h>//不借瓶子void test1(){                 int money=0;                scanf( "%d",&money);                 int bottle=money;                 int drink=money;                                 while(bottle>1)  //剩一个瓶子将陷入死循环                {                                drink+=bottle/2;                                bottle=bottle/2+bottle%2;                }                printf( "%d\n",drink);}//借一个瓶子void test2(){                 int money=0;                scanf( "%d",&money);                 int bottle=money;                 int drink=money;                 while(bottle)                {                                 while(bottle%2==0)  //偶数个瓶子                                {                                                bottle/=2;                                                drink+=bottle;                                }                                 while(bottle%2==1)  //奇数个瓶子                                {                                                bottle+=1;                                                drink+=bottle/2;                                                bottle=bottle/2-1;                                }                }                printf( "%d\n",drink);}int main(){                test1();                test2();                system( "pause");                 return 0;}

结果：

可变参数列表是通过宏来实现的，这些宏定义在stdarg.h头文件中。这个头文件声明了一个类型为va_list的变量和三个宏va_start,va_arg,va_end。我们可以声明一个类型为va_list的变量与这几个宏配合使用，访问参数的值。

函数先声明一个va_list的变量，这个变量通过调用va_start来初始化，第一个参数是va_list变量的名字，第二个参数是省略号前的最后一个有名字的参数。

初始化过程把va_list类型的变量设置为指向可变参数部分的第一个参数。

va_arg宏接受两个参数：va_list变量和参数列表中下一个参数的类型，返回这个参数的值，并使va_list类型的变量指向下一个可变参数。

当访问完最后一个可变参数之后，要调用va_end.

#include <stdio.h>#include <stdlib.h>#include <stdarg.h>float Average(int n,...)  //n是传入参数的个数，int是传入参数的类型{                 int count=n ;                 float sum=0;                 va_list val;                 va_start(val,n );                 while(count--)                {                                sum+= va_arg(val,int );                }                 va_end(val);                 return sum/n ;}void test(){                 float ave=Average(6,1,2,3,4,5,9);                printf( "%f\n",ave);}int main(){                test();                system( "pause");                 return 0;}

结果：

#include <stdio.h>#include <stdlib.h>#include <string.h>void Reverse_str(char * left,char* right){                 while(left <right)                {                                 char tmp=*left ;                                * left=*right ;                                * right=tmp;                                 left++;                                 right--;                }}char* Reverse(char * str){                 char* ret=str ;                 char* start=str ;                 char* end=str +strlen(str)-1;                Reverse_str(start,end);                 while(*str )                {                                start= str;                                 while(*str !=' ' && * str!='\0' )                                                 str++;                                 //str==' '                                end= str-1;                                Reverse_str(start,end);                                 if(*str ==' ')                                                 str++;                }                 return ret;}void test(){                 char s[100]="student a am i" ;                printf( "%s\n",Reverse(s));}int main(){                test();                system( "pause");                 return 0;}

结果：

#include <stdio.h>#include <stdlib.h>unsigned int reverse_bit(unsigned int value ){                 unsigned int tmp=0;;                 unsigned int ret=0;                 for(int i=1;i<=32;i++)                {                                tmp= value & 1;                                ret=ret+(tmp<<32-i);                                 value=value >>1;                }                 return ret;}void test(){                 unsigned int a=25;                printf( "%u\n",reverse_bit(a));}int main(){                test();                system( "pause");                 return 0;}

结果：

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