need help with atoi

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need help with atoi

 
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  #1
Oct 20th, 2009
Hi,
can anyone help me to solve this problem?
I have this code:
c Syntax (Toggle Plain Text) 
  1.   FILE *in; 
  2.   char  i =fgetc(in);
  3.    int perm=0;
  4.    perm =atoi(&i);
  5.    printf("%d\n", perm);
if first character in my "in" file is 2, the output is 28;
if ------------------------------- is 3, -------------- 38, and so on...

any ideas what is wrong with this code?
thanks
Last edited by WaltP; Oct 20th, 2009 at 2:48 am. Reason: Added CODE tags -- with all the help about them, how could you miss using them????
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  #2
Oct 20th, 2009
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Originally Posted by hosh View Post
Hi,
can anyone help me to solve this problem?
I have this code:

FILE *in;
char i =fgetc(in);
int perm=0;
perm =atoi(&i);
printf("%d\n", perm);

if first character in my "in" file is 2, the output is 28;
if ------------------------------- is 3, -------------- 38, and so on...

any ideas what is wrong with this code?
thanks
atoi() accepts a string as argument. Not a character i as it is in your code, nor a pointer to a char like you give it as in atoi(&i)
Something like:
c Syntax (Toggle Plain Text) 
  1. char twenty_three[] = "23";
  2. int result;
  3.  
  4. result = atoi(twenty_three);
Last edited by Aia; Oct 20th, 2009 at 1:13 am.
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  #3
Oct 20th, 2009
.
Last edited by hosh; Oct 20th, 2009 at 2:47 am.
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  #4
Oct 20th, 2009
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any ideas what is wrong with this code?
What exactly is the purpose of your code?
To me it seems like you're reading a file character by character, and then printing out only the digits?

Why doing a conversion to integer if you only want to print the digits out?
C Syntax (Toggle Plain Text) 
  1. char c = fgetc(in); /* read character */
  2. if( isdigit(c) )    /* if character is a digit */
  3.    putchar( c );    /* print character */

Also, if you want to do a conversion to integer for only one digit, then you can use a small trick:
C Syntax (Toggle Plain Text) 
  1. char c = '5';
  2. int i = c - '0'; /* i now contains: 5 */
Please note that you should only apply this trick when you're sure the character variable of which you're subtracting the ASCII value of zero holds a character which is in this range:
'0' <= character <= '9'
You can check on this by using the isdigit() function:
C Syntax (Toggle Plain Text) 
  1. int i;
  2. char c = '9';
  3.  
  4. if( isdigit( c ) )
  5.   i = c - '0'; /* i now contains: 9 */
But again, in your case it seems to me like you don't need a conversion, as it seems like you're just printing digits on your screen, nothing else.

Note: you'll need to include the ctype.h header in order to use the isdigit() function.
"Never argue with idiots, they just drag you down to their level and then beat you with experience."
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  #5
Oct 20th, 2009
Thank you guys.
Now it makes sense...
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