Re: [C]非常郁闷的一个问题

  • From: "Thomas X. Iverson" <txi@xxxxxxxxxxxxx>
  • To: ghostunix@xxxxxxxxxxxxx
  • Date: Thu, 29 May 2008 15:56:34 +0800

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

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