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Topic: USE OF atoi() function (Read 3833 times) |
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syashid
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USE OF atoi() function
« on: Oct 2nd, 2011, 7:42am » |
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plz explain how to divide a number by 3 using only atoi() . also explain this function .how does it works.
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Grimbal
wu::riddles Moderator
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Re: USE OF atoi() function
« Reply #1 on: Oct 3rd, 2011, 1:39am » |
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For "how does it work", just google "man atoi" and read the 1st link.
For example:
char *str = "123";
int n = atoi(str);
returns the integer 123 in n.
I don't see any way to divide an integer by 3 where atoi would be of some help.
You could convert the integer to a string in base 3, drop the last digit and re-convert the string to an integer, but you can't use atoi, it only does base 10.
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SMQ
wu::riddles Moderator
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Re: USE OF atoi() function
« Reply #2 on: Oct 3rd, 2011, 5:43am » |
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Here's a simple -- if not very efficient -- implementation of atoi in case you want to search for a way to use it to divide by 3:
int atoi(const char * p) {
int n;
n = 0;
while (*p >= 48 && *p <= 57) {
n = n*10 + *p - 48;
++p;
}
return n;
}
--SMQ
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syashid
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Posts: 4
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Re: USE OF atoi() function
« Reply #3 on: Oct 3rd, 2011, 8:41am » |
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actually it has been asked in adobe. so a liitle help w'll b good
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Grimbal
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Re: USE OF atoi() function
« Reply #4 on: Oct 3rd, 2011, 10:03am » |
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What language are we talking about?
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websharer
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Re: USE OF atoi() function
« Reply #5 on: Jan 6th, 2012, 5:10pm » |
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on Oct 3rd, 2011, 10:03am, Grimbal wrote:What language are we talking about?
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It's C++.
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TenaliRaman
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I am no special. I am only passionately curious.
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Re: USE OF atoi() function
« Reply #6 on: Jan 6th, 2012, 10:54pm » |
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on Jan 6th, 2012, 5:10pm, websharer wrote:
are you sure its atoi and not itoa?
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Self discovery comes when a man measures himself against an obstacle - Antoine de Saint Exupery
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Stefan Kneifel
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Re: USE OF atoi() function
« Reply #7 on: Feb 2nd, 2012, 12:25pm » |
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Maybe this way:
Code:
#include <stdio.h>
#include <stdlib.h>
int main (int argc, char** argv)
{
unsigned long x, y;
char c[16];
while (--argc)
{
x = y = strtoul(*++argv, 0, 0);
x = (x << 4) + y;
x = (x << 4) + y;
x = (x << 4) + y;
sprintf (c, "%lu0", x);
x = atoi(c) + y;
x >>= 17;
printf ("%lu / 3 = %lu\n", y, x);
}
return EXIT_SUCCESS;
}
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Works up to 49152 / 3 = 16384. However, I think a simple division would be faster 
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| « Last Edit: Feb 2nd, 2012, 12:26pm by Stefan Kneifel » |
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SMQ
wu::riddles Moderator
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Re: USE OF atoi() function
« Reply #8 on: Feb 3rd, 2012, 5:16am » |
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 atoi isn't doing any division in that algorithm. The two lines
sprintf (c, "%lu0", x);
x = atoi(c) + y;
are equivalent to x = x*10 + y;. You're multiplying by 43691 = ({[(16 + 1)*16 + 1]*16 + 1}*10 + 1) then dividing by 131072, and if atoi can be said to be doing anything it's multiplying by 10. The only division happens in the x >>= 17 step.
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