c++ - 如何防止频率表在 C++ 中计算 '' 空框''

Question

我写了下面的代码(用于家庭作业)计算字母和数字并生成一个频率表。我的问题是:当字母或数字不存在时如何停止频率生成？

使用我编写的代码，程序会计算输入的每个字母，但也会为 ASCII 代码中的每个可能的字母/数字发布一行。

希望我的问题问对了，感谢任何帮助或建议!

#include <iostream>
#include <string>

using namespace std;

int countingLetters(string someWords);

int countingNumbers(string someWords);

int frequency(string someWords, double totalChar);

int main() {
    string someWords;
    cout << "Write a some words: " << endl;
    getline(cin, someWords);
    cout << "You wrote:" << someWords << '\n';

    cout << "Your sentence has " << someWords.length() << " characters." << '\n';

    double totalChar = someWords.length();

    cout << "Your sentence has " << countingLetters(someWords) << " letters." << '\n';

    cout << "Your sentence has " << countingNumbers(someWords) << " numbers." << '\n';

    cout << "Frequency of signs and letters :" << endl;

    frequency(someWords, totalChar);


    return 0;
}

int countingLetters(string someWords) {
    int count = 0;
    for (int i = 0; i < someWords.length(); i++) {
        if (someWords[i] >= 'a' && someWords[i] <= 'z')
            count++;
    }
    return count;
}

int countingNumbers(string someWords) {
    int count = 0;
    for (int i = 0; i < someWords.length(); i++) {
        if (isdigit(someWords[i]) != 0)
            count++;
    }
    return count;
}

int frequency(string someWords, double totalChar) {
    cout << " Letter" << '\t' << "Antal" << '\t' << "Procent" << endl;
    int frequency[255]={0};
    for (int i = 0; i < someWords.length(); i++) {
        char c = someWords[i];
        if (isdigit(c) != 0)
            frequency[c]++;
        if (isalpha(c) != 0)
            frequency[c]++;
    }
    for (int i = 0; i < sizeof(frequency); i++) {
        if(frequency[i]>0)
        cout << '\t' << static_cast<char>(i) << '\t' << frequency[i] << '\t' << frequency[i]/totalChar << endl;
    }

    return 0;
}

Answer 1

sizeof(frequency) 是 frequency 数组的大小(以字节为单位)。如果数组除以一个数组元素的字节大小，则您需要元素的数量，即以字节为单位的大小:

这是 frequency 数组的元素数:

sizeof(frequency) / sizeof(frequency[0])

但是当您使用 C++ 时，您不应该使用原始数组，而是 std::array:

#include <array>
...
int frequency(string someWords, int totalChar) {
  cout << " Letter" << '\t' << "Antal" << '\t' << "Procent" << endl;
  std::array<int, 255> frequency{0};

  for (int i = 0; i < someWords.length(); i++) {
    char c = someWords[i];
    if (isdigit(c) != 0)
      frequency[c]++;
    if (isalpha(c) != 0)
      frequency[c]++;
  }

  int x = frequency.max_size();

  for (int i = 0; i < frequency.max_size(); i++) {
    if (frequency[i]>0)
      cout << '\t' << static_cast<char>(i) << '\t' << frequency[i] << '\t' << frequency[i] / totalChar << endl;
  }

  return 0;
}

还有改进的空间。