什么原因导致字符计数不准确，真的很大？ [英] What causes character counts from cin inaccurate and really large?

问题描述

我通过 char c = cin.get（）执行字符计数。我的输出示例为：
a：53
b：32
c：29 等。

I'm doing a character count via char c = cin.get(). Example of my output would be: a: 53 b: 32 c: 29 etc..

对于其中一个字母，我得到一个疯狂的大9位数字。然后，当我使用另一个具有更多字符的输入文件时，数字为6位数，太大以致不准确。这种表型的任何想法？

For one of the alphabets, I'm getting an insanely large 9-digit number. And then when I use another input file that has more characters, the numbers are 6-digits and too large to be accurate. Any thoughts of this phenotype?

再次，对不起，这是学期结束时的紧缩时间。

Again, sorry it's crunch time with the end of the semester. I appreciate any help out there.

int main (int argc, char *argv[])
{

int count [26] = { };   
char alpha [26] = { };

char c;

c = cin.get();     
while(!cin.eof())
{
  if (isalpha(c))
  {
  c = tolower(c);      
  }    

  count [ c - 'a']++;
  alpha [ c - 'a'] = c;

  c = cin.get();
  }     

  for ( int i = 0; i<26; i++ )
     {
     cout << alpha[i] << ":" << count[i] << endl;
     } 

  } //end main    

：（编辑）

a:224
b:50
c:70
d:20
e:167772180
f:10
g:40
h:66
i:28

这里是输入：（编辑）

aaaaaaaaAAAAAaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaBBBB

aaaaaaaaAAAAAaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaAAAaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaBBBB

进行这些更改，但仍然挂起：

Made these changes, but it's still "hanging":

c = cin.get();     
while(c=cin.get())
{
  c = tolower(c);
  if (isalpha(c))
      continue;      


  count [ c - 'a']++;
  alpha [ c - 'a'] = c;

  }     

  for ( int i = 0; i<26; i++ )
     {
     cout << alpha[i] << ":" << count[i] << endl;
     } 

  } //end main    

推荐答案

如果输入文件包含除字母以外的任何内容，任何情况都可能发生，因为您正在访问数组超出边界索引。也许你的意思是：

If the input file contains anyting else than letters, anything can happen because you are accessing the array wtih out of bounds indices. Maybe you meant:

while(!cin.eof())
{
    if (isalpha(c))
    {
        c = tolower(c);      

        count [ c - 'a']++;
        alpha [ c - 'a'] = c;
     }

    c = cin.get();
}     

当您的数据包含换行符（10）时，您正在访问索引为10 - 97 = -87的 alpha 。这可能将10写入 count [4] 的最高有效字节。

E.g. when your data contains a line feed character (10) you are accessing alpha with index 10 - 97 = -87. And this probably writes 10 into the most significant byte of count[4].

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