Thread: learning :) help would be nice

hi i just learned pointers kind of sort of, and the book gave me this example....


#include <iostream>

using std::cout;
using std::endl;

#include <cctype>

void convertToUppercase( char * );

int main()
{
char string[] = "characters and $32.98";

cout << "The string before conversion is: " << string;
convertToUppercase( string );
cout << "\nThe string after conversion is: "
<< string << endl;
return 0;
}

void convertToUppercase( char *sPtr )
{
while ( *sPtr != '\0' ) {

if ( islower( *sPtr ) )
*sPtr = toupper( *sPtr ); // convert to uppercase

++sPtr; // move sPtr to the next character
}
}

i guess this converts the string, characters and $32.98 to upper case, i was just wondering, how could i manipulate which characters get capitolized and which characters dont? just a question my book didnt cover

>how could i manipulate which characters get capitolized

It depends exactly what mean by manipulate which characters get capitalised.

You could split your original string up & capitalise certain sections of it, and recombine it aftwerwards.

Alternatively, you could modify the algorithm to suit what you want to do. For example, you could change it so it only capitalises the starting character of each word. Therefore the string:

"hello world"

becomes

"Hello World"

To do this you will have to check for space characters, and only capatilise the character after. Also capitalise the first character always.

hmm i see, i think i didnt make my question concise enough. lets clarify


say i want to print....


" c programming is fun! "

and i want it to capitolize this way...

"C programming IS fun"

see? i m just curious, how this would be accomplished

I'll say it before the mods get on your case: please use code tags, make life a LOT easier for us to read your code!

Second, this code only makes to uppercase whatever the pointer is pointing to at the time, in this case every letter because the while loop cycles from the beginning to the end hitting every letter. If you want to do every other character, change

Code:

++sPtr;

to

Code:

sPtr+=2;

To pick and choose a little more, you could do something like:

Code:

void convertToUppercase( char *sPtr, int whichOne )
  {
     *sPtr = toupper( *sPtr + whichOne - 1)
  }

if you then wrote convertToUppercase(string, 5) it would uppercase only the 5th character. Not saying that this is the ideal way to do this, but hopefully this will you give you an idea of whats going on. The pointer points to the first character in the string (or the address of technically) and each time its incremented it points to the next letter in the string.

>say i want to print....

>" c programming is fun! "

>and i want it to capitolize this way...

>"C programming IS fun"

I think I follow you now.

You could modify your function so that it specifies a start and range area of the string you want to captilise. Something like:

Code:

void convertToUppercase( char *sPtr, int start, int cnt )
{
  int pos = start;
  while ( pos < start + cnt )
  {
    if ( islower( sPtr[pos] ) )
      sPtr[pos] = toupper( sPtr[pos] ); // convert to uppercase

    pos++;
  }
}

I've haven't compiled this, so there maybe one or two glitches, but the gist of it should be there. I've also use a slight variation of for de-referencing the string pointer on a per char basis because I find this easier, but it should make no difference overall.

Now if your string was:

"c programming is fun!"

calling:

Code:

convertToUpperCase(strPtr, 14, 2);

should change to strPtr to

"c programming IS fun!"

also calling convertToUpperCase(strPtr, 0, 1);

should convert your start character, so that it becomes

"C programming IS fun!"

PJ maybe you should check operator precedence rules. The +whichOne is added to the pointee and not the pointer itself.Not the behaviour you were expecting no doubt

Whoops, you're right, forgot the extra parenthesis there! Shoulda been:

Code:

     *sPtr = toupper( *(sPtr + whichOne - 1));

And depending on whether or not its easier to think of the first character as spot 1 or spot 0 depends on whether or not you care about the "- 1" part.

i understand your logic, but hwne i compiled i got this

y Documents\pointerpractice.cpp(17) : error C2065: 'sPtr' : undeclared identifier.

i dont really understand how its undefined???

for some reason its not letting me compile if i write convertToUppercase ( string, 5 ) or anything of the sort. do i need a special header file???

Post your code again, its hard to say whats going on without seeing it.

ok sorry

#include <iostream>

using std::cout;
using std::endl;

#include <cctype>

void convertToUppercase( char * );

int main()
{
char string[] = "c programming is fun!";

cout << "The string before conversion is: " << string;
convertToUpperCase(strPtr, 14, 2); // error started here
cout << "\nThe string after conversion is: "
<< string << endl;
return 0;
}

void convertToUppercase( char *sPtr, int start, int cnt )
{
int pos = start;
while ( pos < start + cnt )
{
if ( islower( sPtr[pos] ) )
sPtr[pos] = toupper( sPtr[pos] ); // convert to uppercase

pos++;
}
}

and i want it to return " C programming IS fun!"

Ahhh.. he changed variable names on ya

Change this:

Code:

convertToUpperCase(strPtr, 14, 2); // error started here

to this:

Code:

convertToUpperCase(string, 14, 2); // error started here

and that will change the is to IS - if you want to change the c to C you need to make another call your function with parameters 0 and 1 instead of 14 and 2.