C++计算每个字符出现的次数

#include <iostream>
//#include <cstdlib>
#include <ctime>
using namespace std;
 
const int NUMBER_OF_LETTERS = 26;
const int NUMBER_OF_RANDOM_LETTERS = 100;
void createArray(char []);
void displayArray(const char []);
void countLetters(const char [], int []);
void displayCounts(const int []);
 
int main()
{
  char chars[NUMBER_OF_RANDOM_LETTERS];
  createArray(chars);
  cout << "The lowercase letters are:" << endl;
  displayArray(chars);
  int counts[NUMBER_OF_LETTERS];
  countLetters(chars, counts);
  cout << "\nThe occurrences of each letter are:" << endl;
  displayCounts(counts);
 
  return 0;
}
 
void createArray(char chars[])
{
  srand((unsigned int)time(0));
  for (int i = 0; i < NUMBER_OF_RANDOM_LETTERS; i++)
  {
    chars[i] = static_cast<char>('a' + rand() % ('z' - 'a' + 1));
  }
}
 
void displayArray(const char chars[])
{
  for (int i = 0; i < NUMBER_OF_RANDOM_LETTERS; i++)
  {
    if ((i + 1) % 20 == 0)
      cout << chars[i] << " " << endl;
    else
      cout << chars[i] << " ";
  }
}
 
void countLetters(const char chars[], int counts[])
{
  for (int i = 0; i < NUMBER_OF_LETTERS; i++)
    counts[i] = 0;
  for (int i = 0; i < NUMBER_OF_RANDOM_LETTERS; i++)
    counts[chars[i] - 'a']++; //经典
}
 
void displayCounts(const int counts[])
{
  for (int i = 0; i < NUMBER_OF_LETTERS; i++)
  {
    if ((i + 1) % 10 == 0)
      cout << counts[i] << " " << static_cast<char>(i + 'a') << endl;
    else
      cout << counts[i] << " " << static_cast<char>(i + 'a') << " ";
  }
  cout << endl;
}