Check if the String Numeric or Alphabetic

Code

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

void classify_string(const char *str) {
    int alpha = 0;
    int num = 0;
    int c;

    while (c = *str++) {
        if (c >= '0' && c <= '9') {
            num = 1;
        } else {
            c |= 0x20; // convert to lowercase
            if ('a' <= c && c <= 'z') {
                alpha = 1;
            } else {
                alpha = 1;
                num = 1;
                break;
            }
        }
    }

    if (alpha && !num) {
        printf("ALPHABETIC\n");
    } else if (num && !alpha) {
        printf("NUMERIC\n");
    } else {
        printf("MIXED\n");
    }
}

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++;
    }

    classify_string(str);
    return 0;
}

Solving Approach