Conversion from char to int?

  • Thread starter Peon666
  • Start date
  • #1
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Main Question or Discussion Point

What could be wrong with this code?:

Code:
int arr[10];
char arr2[10];
for (int i=0; i<10; i++)
{
        arr[i]=(int)arr2[i];
}
When I output the supposedly converted array, it's outputs some crazy numbers.
???
 

Answers and Replies

  • #2
Filip Larsen
Gold Member
1,256
183
I assume you are using C/C++ here, in which case you should note that automatic variables (variables defined on the stack) are not initialized. Try initialize your character array with some sensible values.
 
  • #3
108
0
It's arr2[10]="P 1 (a tab) 0";
 
  • #4
108
0
And it outputs: 80 49 9 48 0 0 0 0 0 0

I want to get 1 and 0 as integers
 
  • #5
Filip Larsen
Gold Member
1,256
183
Characters are internally represented by a byte that contains the code for the character in question. See for instance http://en.wikipedia.org/wiki/ASCII.

To get the digit of the character you would normally first test if the character is in the range '0' to '9' and then subtract '0'. Something like this:

Code:
char ch = ...;
if (ch >= '0' && ch <= '9') {
  int digit = ch - '0';
  // do whatever you need with digit
}
Alternatively you can use some of the methods from the standard ctype.h library (see for instance http://www.cplusplus.com/reference/clibrary/cctype/).
 
  • #6
D H
Staff Emeritus
Science Advisor
Insights Author
15,393
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It's arr2[10]="P 1 (a tab) 0";
And it outputs: 80 49 9 48 0 0 0 0 0 0
80 = 'P'
49 = '1'
9 = tab
48 = '0'
0 = end of string

It is working exactly right, assuming you are working on an ASCII machine.

I want to get 1 and 0 as integers
Then you want to do something other than a simple cast.
 
  • #7
108
0
Alright. The problem is solved to some extend. But a little more problem:

For the given string [P 1 (tab) 0] it outputs fine: 1 0
But when I have a string [P 2 (tab) 34] it outputs: 2 3 (no four.)

What could be the problem?
 
  • #8
D H
Staff Emeritus
Science Advisor
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You need to learn how to parse. Casting is not what you want here.
 
  • #9
D H
Staff Emeritus
Science Advisor
Insights Author
15,393
683
To add to the above:

In this case, the function sscanf() will do the trick.

For more complicated parsing problems, you will probably need to learn how to use things like strtok() to split the string into tokens and things like strtol() to convert the numeric tokens into integers.
 

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