Check if the String Numeric or Alphabetic

Code

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

void classify_string(const char *str) {
    // Your logic here
    int len = -1;
    while(str[++len] != '\0');

	if(len == 0)
	{
		printf("MIXED");
		return;
	}
    bool isDigit = true;
    bool isAlpha = true;

    for(int i=0; i<len; ++i)
    {
        if(((str[i] >= 'a') && (str[i] <= 'z')) || ((str[i] >= 'A') && (str[i] <= 'Z')))
        {
            isDigit = false;
        }
        else if((str[i] >= '0') && (str[i] <= '9'))
        {
            isAlpha = false;
        }
        else
        {
            isDigit = false;
            isAlpha = false;
            break;
        }
    }

    if(isAlpha)
    {
        printf("ALPHABETIC");
    }
    else if(isDigit)
    {
        printf("NUMERIC");
    }
    else
    {
        printf("MIXED");
    }
}

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