Having trouble with homework lesson 16 (ah.. pointers..)

[Clodi]

I am trying to solve the bit where we are supposed to reverse a string a print it on screen.
Here is my approach:

This is O.K.

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void putString( const char* pChar )
{
	for ( ; *pChar != 0 ; pChar ++ )
	{
		putchar( *pChar );
	}
}

This is also O.K.

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void getString( char* pChar, int MaxLength )
{
	char c = 0;
	char index = 0;

	for ( ; index < MaxLength && c != '\n' ; index ++ )
	{
		c = getchar();
		*( pChar + index ) = c;
	}
	*( pChar + index ) = '\0';
}

This is where the problem is..

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void revString( char* pChar )
{
	//create a copy of the buffer somewhere else in memory
	char Buffer[127];

	//point to the first guy
	char* pBuff = &Buffer[0];

	//copy first buffer (in main) to buffer in this function
	for ( char index = 0; *( pChar + index ) != 0; index ++ )
	{
		Buffer[ index ] = *( pChar + index );
	}

	//point to the last guy
	for ( ; *pBuff != 0; pBuff ++ );


	//run through (main) buffer and replace each letter with the reverse
	//that is achieved by accessing second (function) buffer other way round
	for ( ; *pChar != 0; pChar ++ )
	{
		for ( char index = 0; *( pBuff + index ) < 127 && *( pBuff + index ) > (-128) ; index -- )
		{
			*pChar = *( pBuff + index );
		}
	}
}

and this is the main.. again, the issue is above

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void main()
{
	putString( "Welcome to America\nType in some shit: " );
	char Buffer[127];
	getString( &Buffer[0],127 );

	putString( "Here's your string: " );
	putString( &Buffer[0] );

	putString( "And now reversed: " );
	revString( &Buffer[0] );
	putString( &Buffer[0] );
}

[LuisR14]

ok here's your problem

1. you're checking that the value pointed by *(pBuff + index) is less than 127 and greater than -128

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	for ( char index = 0; *( pBuff + index ) < 127 && *( pBuff + index ) > (-128) ; index -- )

when it should be checking that index is greater than -128
but since the index into the pointer below can't be negative the above would have to start from 127 to 0

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		*pChar = *( pBuff + index );

2. you're looping thru the string and setting the same last value into the reversed pChar string

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	for ( ; *pChar != 0; pChar ++ )
	{
		for ( char index = 0; *( pBuff + index ) < 127 && *( pBuff + index ) > (-128) ; index -- )
		{
			*pChar = *( pBuff + index );
		}
	}

but since problem 1. is happening you're actually putting in some undefined value (or garbage lol)

[Clodi]

Thank you so much,

But why is this one not working??

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void revstring( int* p )
{
	int index;
	for ( index = 0; *( p + index ) != 0; index ++ );
	int* pEnd = ( p + index );

	while (pEnd >= p )
	{
		int a = 0;
		a = *p;
		*p = *pEnd;
		*pEnd = a;
		p ++;
		pEnd --;
	}
}

[LuisR14]

i believe it's because you're using int* instead of char* o.o
what you have there would work fine with char*

edit: actually, it's something else that's causing it to not work xP
you're copying over the null character from the end of the string to the beginning

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	for ( index = 0; *( p + index ) != 0; index ++ );
	int* pEnd = ( p + index );

simple solution tho (let's see if you figure it out tho )

[Clodi]

thank you so much : )

tonight i ll look into it. I really want to get it to work !!