Re: [C]非常郁闷的一个问题

  • From: "Ben Ben" <daihuxyz@xxxxxxxxx>
  • To: ghostunix@xxxxxxxxxxxxx
  • Date: Thu, 29 May 2008 14:38:04 +0800

弄的我也想学习C了。可是时间不多。现在上班了

On 5/29/08, 李磊 <lilei1008@xxxxxxxxx> 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
>>
>>
>

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