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type conversion C, atoi()


 
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# 1  
Old 12-07-2011
type conversion C, atoi()

In the book "The C programming language"; second edition, chapter 2.7 there is a snippet which is supposed to:
"convert a string of digits into its numeric equivalent".
Code:
int atoi(char s[])
{
    int i, n;

    n = 0;

    for ( i = 0; s[i] >= '0' && s[i] <= '9'; ++i)
        n = 10 * n + (s[i] - '0')

    return n;
}

What is the purpose to run
Code:
10 * n

if n is 0 ?

thanks
# 2  
Old 12-07-2011
Simplifies the code. If not done this way, you would have to have extra code to handle the n = 0 case.
This User Gave Thanks to fpmurphy For This Post:
# 3  
Old 12-08-2011
Ok, thanks. What i don't understand: Is there a difference between
Code:
0  * 0 
 1 * 0 
... 
10 * 0

in C ? Different: is the 10 arbitrary, or is it chosen for a reason?
# 4  
Old 12-08-2011
Hi friend,

The code is not only for n=0, its in a for loop. Let me explain with an example.

If s contain a string "5270", then the loop continue for 4 times:

1st : 10*0 + 5 = 5
2nd : 10*5 + 2 = 52
3rd : 10*52 + 7 = 527
4th : 10*527 + 0 = 5270
which is the n value and a number instead of string.

Try to use some debugging tools and check the variables, u will understand it clearly...
This User Gave Thanks to siva shankar For This Post:
# 5  
Old 12-08-2011
Thanks to both of you, i understand it much better now (now fully, but i am on my way). Yes, siva shankar, what you just explained is exactly what i did not see.

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