function getinteger from kernighan ritcie book

[kalar]

The following loop fills an array with integers by calls to getint
[PHP]int main(void)
{
int n, array[SIZE], getint(int *);

for(n=0; n<SIZE && getint(&array[n]) !=EOF; n++)
;

return 0;
}


/*int getch(void);
void ungetch(int);*/ ignore it

int getint(int *pn)
{
/* int c,sign;

while(isspace(c=getch()))
;
if(!isdigit(c) && c!=EOF && c!='+' && c!='-'){
ungetch(c);
return 0;
}

sign = (c == '-') ? -1 : 1;
if(c == '+' || c == '-')
c=getch();*/ ignore it
for(*pn = 0; isdigit(c); c = getch())
*pn = 10* *pn + (c - '0');
*pn *= sign;
if (c!=EOF)
ungetch(c);

return c;
}
[/PHP]

In line 5 we have a loop that fills the array with integers.Then in line 29 we have another loop that returns the integers in the array.But i don't understand line 30, why we use 10* *pn?? In position of getch we can put getchar.Thanks

[JosAH]

In line 5 we have a loop that fills the array with integers.Then in line 29 we have another loop that returns the integers in the array.But i don't understand line 30, why we use 10* *pn?? In position of getch we can put getchar.Thanks

That function takes a pointer to an int where the result is supposed to be stored.
Suppose the characters '1', '2' and '3' are read from the input stream. First the
value '1'-'0' == 1 is stored in that location, the next loop pass multiplies that
value by 10 and add the new value '2'-'0' == 2; so the result is 10+2 == 12.
The third loop pass does the same and the result is 12*10+3 == 123, exactly
what you wanted.

kind regards,

Jos

[kalar]

The third loop pass does the same and the result is 12*10+3 == 123, exactly
what you wanted.

kind regards,

Jos

yes but we want separately the '3' on array[2] and not 123.Or you mean that we type '123' as one number? I don't understand.Sorry

[JosAH]

yes but we want separately the '3' on array[2] and not 123.Or you mean that we type '123' as one number? I don't understand.Sorry

Well, you've copied the wrong function for your purposes then. You could change the body of the loop in that function to:

*pn++= c-'0';
 

... but you have to take some precautions w.r.t. buffer (array) overflow then.

kind regards,

Jos

[kalar]

edit:
sorry my mistake now i found it

[JosAH]

I don't think so
A) because the function is from kernighan and ritcie book and i don't find any mistake in the errata list from the book
B)and mainly
then why works both af them correct(also *pn++= c-'0'; worked with the same result)??

A) I immediately agree that there are no errors in that little function but it doesn't
do what you had in mind (see your previous reply). You have to make up your
mind: do you want:

A1) the three characters 123 to be interpreted as the single integer value 123 or
A2) do you want three separate integer values 1, 2 and 3?

B) I don't believe that K&Rs original version and my quick hack yield the same result.

kind regards,

Jos

[kalar]

A) I immediately agree that there are no errors in that little function but it doesn't
do what you had in mind (see your previous reply). You have to make up your
mind: do you want:

A1) the three characters 123 to be interpreted as the single integer value 123 or
A2) do you want three separate integer values 1, 2 and 3?

B) I don't believe that K&Rs original version and my quick hack yield the same result.

kind regards,

Jos

As i said my mistake.I try the same numbers in the two functions
1 enter
2 enter
3 enter
.
.
.
So i had the same result.Now i understand it(how work both functions).Thanks again