75. Count Alphabets Digits and Symbols in a String

#include <stdio.h>
#include <stdint.h>

void classify_chars(const char *str, uint8_t *alpha, uint8_t *digit, uint8_t *symbol) {
    *alpha = 0;
    *digit = 0;
    *symbol = 0;

    uint8_t i = 0;
    while (str[i] != '\0') {
        char ch = str[i];
        if ((ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z')) {
            (*alpha)++;
        } else if (ch >= '0' && ch <= '9') {
            (*digit)++;
        } else if (ch != ' ') {
            (*symbol)++;
        }
        i++;
    }
}

int main() {
    char str[101];
    fgets(str, sizeof(str), stdin);
    // Remove newline
    uint8_t i = 0;
    while (str[i]) {
        if (str[i] == '\n') {
            str[i] = '\0';
            break;
        }
        i++;
    }
    uint8_t alpha = 0, digit = 0, symbol = 0;
    classify_chars(str, &alpha, &digit, &symbol);
    printf("Alphabets = %u\nDigits = %u\nSymbols = %u", alpha, digit, symbol);
    return 0;
}

What is this about?

Basic parsing problem that mimics real firmware needs like command validation, serial input checks, or debugging interfaces.

Why it matters in firmware?

• ctype.h may not be available or used due to overhead
• MCU serial handlers often need raw character classification
• Helps structure CLI, command parser, or telemetry checks

Solution Logic

• Use ASCII ranges:
  
  • A-Z = 65 to 90
  • a-z = 97 to 122
  • 0–9 = 48 to 57
• Any other non-space character is a symbol