Check if the String Numeric or Alphabetic

Code

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

void classify_string(const char *str) {
    int num = 0;
    int alpha = 0;
    int sign = 0;
    int size = 0;
    while(str[size]!='\0')
    {
        size++;
    }
    for(int i=0;i<size;i++)
    {
        if(str[i]>='0' && str[i]<='9')
        {
            num++;
        }
        else if((str[i]>='a' && str[i]<='z') || (str[i]>='A' && str[i]<='Z'))
        {
            alpha++;
        }
        else
        {
            sign++;
        }
    }

    if(num==0 && alpha!=0 && sign==0)
    {
        printf("ALPHABETIC");
    }
    else if(num!=0 && alpha==0 && sign==0)
    {
        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