Creating a visual representation of character frequencies requires managing three core components: storage mechanisms, input processing, and rendering logic. When focusing on uppercase English letters, a fixed-size array offers efficient storage compared to associative containers.

Input handling should robustly capture stream data until the end-of-file signal. Each character is validated to ensure it falls within the target range before updating the corresponding counter. Tracking the maximum frequency during ingestion allows the rendering phase to determine the graph's vertical scale dynamical.

The visualization process iterates from the highest frequency down to one. For each vertical level, the program checks every letter's count. If a letter's frequency meets or exceeds the currant level, a marker is printed; otherwise, a space maintains alignment. Columns are separated by whitespace for readability, and the alphabet labels are printed once the bars are complete.

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main() {
    vector<int> counts(26, 0);
    char ch;
    int max_height = 0;

    while (cin.get(ch)) {
        if (ch >= 'A' && ch <= 'Z') {
            int index = ch - 'A';
            counts[index]++;
            if (counts[index] > max_height) {
                max_height = counts[index];
            }
        }
    }

    for (int level = max_height; level > 0; --level) {
        for (int k = 0; k < 26; ++k) {
            if (counts[k] >= level) {
                cout << "*";
            } else {
                cout << " ";
            }
            if (k < 25) cout << " ";
        }
        cout << "\n";
    }

    for (int k = 0; k < 26; ++k) {
        cout << (char)('A' + k);
        if (k < 25) cout << " ";
    }
    cout << endl;

    return 0;
}

Execution involves piping text into the standard input. The program filters non-uppercase characters and constructs the grid based on the highest occurrence count. The final output displays the vertical bars followed by the corresponding letter labels on the bottom row.