Why does casting char to int produce unexpected values in C++?

[Peon666]

What could be wrong with this 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.
?

 

[Filip Larsen]

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.

 

[Peon666]

It's arr2[10]="P 1 (a tab) 0";

 

[Peon666]

And it outputs: 80 49 9 48 0 0 0 0 0 0

I want to get 1 and 0 as integers

 

[Filip Larsen]

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:

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/).

 

[D H]

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.

 

[Peon666]

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?

 

[D H]

You need to learn how to parse. Casting is not what you want here.

 

[D H]

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.