Can we set a variable to a number range in C? - c

Question

What I'm thinking of is something like this:
range = range <= '9' && range >= '0';
I want to extract a contiguous sequence of digits from a string. And once the program find a non-digit after it finds the sequence of digits, I want it to break out of the loop using break; in the second if-statement (line 59). And I think it would be much easier if I can just write the condition using a variable.
What I want to say in line 59 is "If the var digit_flag is TRUE and the element in the array s is included in the var range(which is a number range), then break;"
Can it be done?
If it can't, why not?
int i = 0;
int size_of_s = 0;
int digit_flag = FALSE;
while (s[i] != '\0') {
if (s[i] == ' ') {
i++;
} else if (s[i] <= '9' && s[i] >= '0') {
size_of_s++;
i++;
digit_flag = TRUE;
}
if (digit_flag == TRUE && s[i] != range) {
break;
}
}

Answer 1

What I want to say in line 59 is "If the var digit_flag is TRUE and the element in the array s is included in the var range(which is a number range), then break;"
Can it be done?
As far as I know this can not be done in C.
If it can't, why not?
Because there is no relational or comparison operator in the C language which means "operand 1 is within the range of operand 2" (even if the second operand is an array). You need to use a logical AND (&&) of two conditions (>= A, <= B).
If you don't want to use a standard function - such as isdigit(), which will use the range 0-9 - you could use a macro
#define IS_IN_RANGE(x, min, max) (x >= min && x <= max)
or inline function.
static inline int is_in_range(int x, int min, int max) {
return (x >= min && x <= max);
}

Answer 2

If you want a "range" in C, you have to create one yourself:
// integer range class
// in this case it could also be a char range
struct int_range {
int start;
int end;
};
// range method to test for inclusinon
// in this case range could be passed as value efficiently, too,
// but passing as const pointer is more generic, so better example
bool int_range_contains(const struct int_range *range, int value) {
return value >= range->start && value <= range->end;
}
// example usage
void func(void) {
struct range digit_chars = { '0', '9' };
int character = 'a';
if (int_range_contains(&digit_chars, character)) {
// something
}
}
Of course this is a total overkill for this case. Your current if (s[i] <= '9' && s[i] >= '0') is better, and every C programmer immediately sees what's going on there.

Answer 3

Instead of
digit_flag == TRUE && s[i] != range
you can re-use what you already wrote
digit_flag == TRUE && !(s[i] <= '9' && s[i] >= '0')

Answer 4

If you want to extract the number sequence part in a string like
char str[]="hello1234isthesequence.";
you could just do
char seq[30];
if( sscanf(str, "%*[^0-9]%[0-9]", seq)==1 )
{
printf("\nThe sequence is: %s", seq);
}
where the %*[^0-9] is used to read everything from str[] till a non-digit character is encountered and the * is to suppress it ie, it will be discarded and won't be assigned to anywhere.
Next the %[0-9] will read the remaining part of the string in str till and excluding non-number and assign it to seq.
sscanf() will return the number of total successful assignments that it made, which in this case should be 1.
You may change the size of seq as per the size of the input string and change the width specifier in the format string of scanf() to avoid overflow.