Re: [C]非常郁闷的一个问题

  • From: "菜小镇" <cainiao55@xxxxxxxxx>
  • To: ghostunix@xxxxxxxxxxxxx
  • Date: Thu, 29 May 2008 18:35:41 +0800

建议跳河

在08-5-29,Ken. xu. SourceForge <xzknet@xxxxxxxxxxxxxxxxxxxxx> 写道:
>
> 自杀吧
>
> 在08-5-29,Thomas X. Iverson <txi@xxxxxxxxxxxxx> 写道:
>>
>> On Thursday 29 May 2008 13:30:32 李磊 wrote:
>> > 2008/5/29 Thomas X. Iverson <txi@xxxxxxxxxxxxx>:
>> >
>> > > 在做一道指针的习题,要求输入任意多个浮点数进行平均数的计算,动态分配内存
>> > > 书上的代码如下:
>> > > /* Exercise 7.1 Calculating a floating-point average using pointers */
>> > > /*********************************************************************
>> > >  * In this solution we allocate a some memory and when it is full    *
>> > >  * allocate a new, larger amount of memory and copy the contents of  *
>> > >  * the old memory to the new. We then free the old memory. This      *
>> > >  * process repeats as often as necessary.                            *
>> >
>> >  *********************************************************************/
>> > > #include <stdio.h>
>> > > #include <stdlib.h>
>> > > #include <ctype.h>
>> > >
>> > > int main(void)
>> > > {
>> > >  double *values = NULL;     /* Pointer to memory holding data values
>> > > */
>> > >  double *temp = NULL;       /* Pointer to newly allocated memory
>> > > */
>> > >  double sum = 0.0;          /* Sum of values
>> > > */
>> > >  int capacity = 0;          /* Maximum number of values that can be
>> stored
>> > > */
>> > >  int increment = 5;         /* Capacity increment for dynamic
>> allocation
>> > > */
>> > >  int count = 0;             /* Number of values read
>> > > */
>> > >  int i = 0;                 /* Index to array
>> > >  */
>> > >  char answer = 'n';
>> > >
>> > >  do
>> > >  {
>> > >    if(count == capacity)    /* Check if there is spare memory */
>> > >    {
>> > >      capacity += increment; /* Increase the capacity of memory by
>> increment
>> > > */
>> > >      temp = (double*)malloc((capacity)*sizeof(double)); /* and
>> allocate it
>> > >  */
>> > >      if(temp == NULL)       /* If memory was not allocated */
>> > >      {                      /* Output a message  and end   */
>> > >        printf("Memory allocation failed. Terminating program.");
>> > >        exit(1);
>> > >      }
>> > >      if(values == NULL)     /* Are there any
>> values?                  */
>> > >        values = temp;       /* No - so just copy address of new memory
>> */
>> > >      else                   /* Yes - so copy data from old to
>> new      */
>> > >      {
>> > >        for(i = 0 ; i<count ; i++)
>> > >          *(temp+i) = *(values+i);
>> > >        free(values);        /* Free the old memory */
>> > >        values = temp;       /* Copy address of new */
>> > >      }
>> > >      temp = NULL;           /* Reset pointer       */
>> > >    }
>> > >
>> > >    printf("Enter a value: ");
>> > >    scanf("%lf", values+count++);
>> > >
>> > >    printf("Do you want to enter another(y or n)? ");
>> > >    scanf(" %c", &answer);
>> > >  }while(tolower(answer) == 'y');
>> > >
>> > >  /* Now sum the values */
>> > >  for(i = 0 ; i<count ; i++)
>> > >    sum += *(values+i);
>> > >
>> > >  /* Output the average */
>> > >  printf("\n The average of the the values you entered is %.2lf.\n",
>> > > sum/count);
>> > >  free(values);     /* We are done - so free the memory */
>> > > }
>> > >
>> > > 在理解了这个算法后,我自己重新实现了一遍(算是默写性质的复习):
>> > >
>> > > #include<stdio.h>
>> > > #include<stdlib.h>
>> > > #include<ctype.h>
>> > >
>> > > int main(void)
>> > > {
>> > >        double *temp=NULL;
>> > >        double *value=NULL;
>> > >        double sum=0.0;
>> > >        int i;
>> > >        int count=0;
>> > >        int capa=0;
>> > >        int incre=5;
>> > >        char answer='n';
>> > >
>> > >        do
>> > >        {
>> > >                if(count==capa)
>> > >                {
>> > >                        capa+=incre;
>> > >                        temp=(double *)malloc((capa)*sizeof(double));
>> > >                        if(temp==NULL)
>> > >                        {
>> > >                                printf("Failed\n");
>> > >                                return 1;
>> > >                        }
>> > >                        if(value==NULL)
>> > >                                value=temp;
>> > >                        else
>> > >                        {
>> > >                                for(i=0;i<count;i++)
>> > >                                {
>> > >                                        *(temp+i)=*(value+i);
>> > >                                }
>> > >                                free(value);
>> > >                                value=temp;
>> > >                        }
>> > >                        temp=NULL;
>> > >                }
>> > >                printf("Enter a value:");
>> > >                scanf("%lf",value+count++);
>> > >                printf("Enter another?:");
>> > >                scanf(" %c",&answer);
>> > >        }while(tolower(answer)=='y');
>> > >
>> > >        for(i=0;i<count;i++);
>> >
>> > 狂晕.............检查下这句.......
>> >
>> > >
>> > >        {
>> > >                sum+=*(value+i);
>> > >        }
>> > >        printf("%.2lf",sum/count);
>> > >        free(value);
>> > > }
>> > >
>> > > 问题出现了,这两段代码我怎么看都没有觉得有问题,可是就是有两个问题:
>> > > 1.我自己写的这个代码无法很好的处理scanf输入缓冲问题
>> > >
>> 2.我自己写的这个代码计算出的平均值总是0,我后来加了个printf查看sum和count的值,sum总是为0,count没有问题,不知道为什么
>> > >
>> > >
>> > > --
>> > > Keep It Simple Stupid
>> > > http://blog.ghostunix.org
>> > > ghosTM55
>> > >
>> > >
>> >
>>
>> 我靠。。。竟然犯这种错误,不能原谅自己......
>>
>> --
>> Keep It Simple Stupid
>> http://blog.ghostunix.org
>> ghosTM55
>>
>>
>
>
> --
> ---------------------------签名---------------------------
> 有信心不一定会成功→没信心一定不会成功
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