通读文件中的字符并计算有多少个单独的字母 [c++]

Question

所以用户将输入一个包含任何文本的文件，程序需要通读每个字符并计算每个字符的数量（仅限大写和小写字母）。所以，可能有 50 个 A，23 个 b，等等......

这是我目前在 main.cc 中的内容：

    char character;
    int i = 65; //this is the iterator to go through upper and lowercase letters
    int count = 0; //counts number of characters and resets when exiting the loop and after using cout
    ifstream file(filename); //filename is a string the user inputs
    while (i != 0) {
        while (file >> character) {
            int a = character;
            cout << a << endl; //testing: outputs the correct number for the letter
            if (i == a) { //but for some reason this part isn't working?
                count++;
            }
        }
        cout << count << endl; //this outputs 0 every time
        count = 0;
        i++;
        if (i == 91)  i = 97;  //switch to lower case
        if (i == 123) i = 0;   //exit loop
    }

感谢您的帮助！谢谢:)

Answer 1

让我们假设文本是 ASCII 或扩展 ASCII，因此最多有 256 个可能的字符。

您可以使用数组来保存给定字符的出现次数。每个插槽对应一个字符；相反，字符可以用作数组的索引。

例子：

unsigned int MAXIMUM_CHAR_VALUES = 256U;
unsigned int occurrences[MAXIMUM_CHAR_VALUES] = {0};
char c;
while (my_text_file >> c)
{
  ++occurrences[c];
}
// Print them out
for (unsigned int i = 0; i < MAXIMUM_CHAR_VALUES; ++i)
{
  if (!isprint(i))
  {
    cout << "0x" << hex << i;
  }
  else 
  {
    c = static_cast<char>(i);
    cout << c;
  }
  cout << ":  " << occurrences[i] << "\n";
}

如果您必须使用“节点”，您可以将数组更改为节点数组。

还有其他可以使用的结构，例如二叉树。

Answer 2

这是使用地图的理想场所

从文件中读取一个字符

file >> character;

地图位置的增量

if( isalpha(character) ) { myMap[character]++; }

最后，您可以遍历所有地图条目并将它们全部打印出来。

for(map<char, int >::const_iterator it = myMap.begin(); it != myMap.end(); ++it)
{    
    std::cout << "The character " << it->first << " was found " << it->second<< " times." << std::endl;
}

Answer 3

感谢其他答案，我想出了这种方法......到目前为止它工作得很好。谢谢各位！

char character;
int a[256] = {0};
int i = 65;
ifstream file(filename);

while (file >> character) {
    a[character]++;
}

while (i != 0) {
    character = i;
    cout << "There are " << a[i] << " of " << character << endl;
    i++;
    if (i == 91) i = 97;
    if (i == 123) i = 0;
}