Is Text Box data check possible?

#include <acknex.h>
#include <default.c>

#define PRAGMA_POINTER

STRING *non_numeric_str = "0123456789a";
STRING *numeric_str = "5325";
STRING *empty_str = "";

// receives a STRING and position (num) of a character in that STRING
// returns a single character as a STRING
STRING *get_next_char(STRING *src_str, int num)
{
	if(!src_str)
	{
		return NULL;
	}
	
	if(num > str_len(src_str))
	{
		return NULL;
	}
	
	STRING *temp_str = "";
	str_cpy(temp_str, src_str);
	str_trunc(temp_str, str_len(src_str) - num);
	str_clip(temp_str, num - 1);
	
	return temp_str;
}

// returns TRUE (1) if string is numeric
// otherwise returs FALSE (0)
var is_numeric_str(STRING *src_str)
{
	if(!src_str)
	{
		return false;
	}
	
	int i = 0, j = 0, res = true;
	
	for (i = 0; i < str_len(src_str); i++)
	{
		STRING *temp_str = get_next_char(src_str, i + 1);
		
		for (j = 0; j < 10; j++)
		{
			if (!str_cmpi(temp_str, str_for_num(NULL, j)))
			{
				res = false;
				continue;
			}
			
			res = true;
			break;
		}
		
		if(res == false)
		{
			break;
		}
	}
	
	return res;
}

// returns TRUE (1) is string's length is zero
// otherwise returns FALSE (0)
var is_empty_str(STRING *str)
{
	if(!str)
	{
		return false;
	}
	
	if(str_len(str) > 0)
	{
		return false;
	}
	else
	{
		return true;
	}
}

// main game function
void main()
{
	var numeric1 = is_numeric_str(non_numeric_str);
	var numeric2 = is_numeric_str(numeric_str);
	var empty = is_empty_str(empty_str);
	
	while(!key_esc)
	{
		DEBUG_VAR(numeric1, 0);
		DEBUG_VAR(numeric2, 20);
		DEBUG_VAR(empty, 40);
		
		wait(1);
	}
}

#include <acknex.h>


STRING* defstr="#100";
STRING* test_str="";


//is input box open
int is_input_box_on=0;

//test variable
int test_num;

//debug
function textx_startup()
{
	while(1)
	{
		if(is_input_box_on==1)
		{
			draw_text("Enter any number",1,1,COLOR_GREEN);
			draw_text(test_str,1,200,COLOR_GREEN);

			
		}
		DEBUG_VAR(test_num,20);
		wait(1);
	}
}

function on_f1_event() 
{
	beep();
	
	//clear all strings

	str_cpy(test_str,"");
	test_num=0;
	

	

	char this_char = 0;
	is_input_box_on=1;
	
	while(this_char!=13)//wait until press enter
	{
		

		this_char = inchar(defstr);
		if(this_char!=1)  
		{
			//if is numeric
			if(str_stri(this_char,"0")||
			str_stri(this_char,"1")||
			str_stri(this_char,"2")||
			str_stri(this_char,"3")||
			str_stri(this_char,"4")||
			str_stri(this_char,"5")||
			str_stri(this_char,"6")||
			str_stri(this_char,"7")||
			str_stri(this_char,"8")||
			str_stri(this_char,"9"))
			{
				str_cat(test_str,defstr);
				
			}
			else
			{
				//if isn't numeric don't do anything
			}
			
		}
		wait(1);
	}

	//convert string to number
	test_num=str_to_int(test_str);
	
	//turn of the box
	is_input_box_on=0;

	
	//if bigger than 100
	if(test_num>100)
	{
		printf("Error: Value is bigger than 100!");
		
		//try again
		on_f1_event(); 
	}

}




function main()
{

	on_f1_event();
}
void on_esc_event()
{
	sys_exit("");
}