Character Classification Logic

To count vowels and consonants accurately:

1. Traverse the string character by character until the null terminator \0.
2. Convert each character to lowercase using tolower().
3. Check if it matches a, e, i, o, u (vowels).
4. If it is an alphabetic character but not a vowel, count it as a consonant.

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C Source Code

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>
#include <ctype.h>

void countCharacters(const char *str, int *vowels, int *consonants, int *digits, int *spaces) {
    *vowels = *consonants = *digits = *spaces = 0;

    for (int i = 0; str[i] != '\0'; i++) {
        char ch = tolower((unsigned char)str[i]);

        if (ch >= 'a' && ch <= 'z') {
            if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u') {
                (*vowels)++;
            } else {
                (*consonants)++;
            }
        } else if (isdigit((unsigned char)str[i])) {
            (*digits)++;
        } else if (isspace((unsigned char)str[i])) {
            (*spaces)++;
        }
    }
}

int main() {
    const char text[] = "Modern C23 Standard Edition 2026";
    int v, c, d, s;

    countCharacters(text, &v, &c, &d, &s);

    printf("Input Text: \"%s\"\n\n", text);
    printf("  Vowels:      %d\n", v);
    printf("  Consonants:  %d\n", c);
    printf("  Digits:      %d\n", d);
    printf("  Spaces:      %d\n", s);

    return 0;
}

Sample Output

text (ISO Standard)
Copy
Input Text: "Modern C23 Standard Edition 2026"

  Vowels:      9
  Consonants:  15
  Digits:      6
  Spaces:      4

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Complexity Analysis

• Time Complexity: O(n) where n is string length.
• Space Complexity: O(1) constant memory overhead.

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Related Programs

• Reverse character strings in String Reverse in C.
• Review standard library functions in C Standard Library Functions.