test.cpp

char* humanlizeString(const char *str) {
    char *result = new char[strlen(str) * 10];

    const char *name[] = {
        "nghin", "trieu", "ti"
    };
    const char *number[] = {
        "khong", "mot", "hai", "ba", "bon",
        "nam", "sau", "bay", "tam", "chin"
    };
    const char *name2[] = {
        "", "muoi ", "tram "
    };
    
    int n = strlen(str);
    int readnum;
    int pos = 0;
    int prefix;
    char *tmp = new char[100];

    while(n != 0) {
        readnum = n % 3 == 0 ? 3 : n % 3;

        for(int i = pos, j = pos + readnum; i < j; i++) {
            tmp[0] = '\0';
            if(j - i == 2 && str[i] - '0' == 0) {
                strcat(result, "le ");
                continue;
            }
            else {
                strcat(tmp, number[ str[i] - '0' ]);
            }
            
            strcat(tmp, " ");
            strcat(result, tmp);            
            
            if(j - i != 0) 
                strcat(result, name2[j - i - 1]);
        }
        
        prefix = n % 3 == 0 ? (n - 1) / 3 : n / 3;
        while(prefix > 3) {
            prefix = prefix - 3;
        }
        if(prefix - 1 >= 0) {
            strcat(result, name[prefix - 1]);
            strcat(result, " ");
        }

        
        pos = pos + readnum;
        n -= readnum;
    }

    return result;
}