Passing Values Question...

**tinkerbell20** · 06-25-2005

Hi Everyone!

This is my question...
The following program segmant asks the user for his or her first name in main(). Write a function that reverses the name in the array so that main() can print the reversed name. To make it easy, assume that the user name is always five characters long ("Jerry" or "Peter", for example).

Code:

#include <iostream.h> // I know it's the old method, but that's what's the book writes
rev(char name[6]);

main()
{
     char name[6];
     cout << "What is your first name (5 letters, please)? ";
     cin  >> name;

     rev(name);
     cout << "Your name spelled backwards is " << name << "\n";
     return 0;
}
//from here is what I added
rev(char name[6])
{
      name[0] = name[4];
      name[1] = name[3];
      name[3] = name[1];
      name[4] = name[0]; 
      return 0;
}

Is there a way to write it with a loop? My way doesn't work--the last character doesn't change

Thanks all.

Tinker.

**Jaken Veina** · 06-25-2005

Well, that's because by the time you get to the last statement in your rev() function, name[0] has already been changed. It no longer stores the first number in the name. You assigned name[4] to it. This is a very common problem. The simplest way to understand is to make a copy of the string. See if you can't figure it out yourself with that much to work with.

And yes, there is a way to loop that. And that would probably be best, since it'll make it easier for you to modify later on, so that you can accept any length of name.

I also notice that you have failed to specify a return value for both of your functions. Not a good idea.

**~~ILoveVectors~~** · 06-26-2005

you could just use strrev();
that would make your life easier no matter what size the
array was.

search google for a more indepth example but it use is pretty
straight forward

Code:

char array[50];
char array2[50];
array2 = strrev(array);

**JoshR** · 06-26-2005

Ya you could do it in a loop, this is just code off the top of my head, but you could add to it etc...

Code:

...
...
string buffer = "test";
string bufferReversed;

for (int loop = buffer.size()-1; loop >= 0; loop--)
   bufferReversed += buffer[loop];

return bufferReversed;

Btw, i know you are working with char arrays, but you could adapt this technique to it, by creating a bufferReversed array with the same size as buffer, and then instead of += have there be an extra incrementing variable inside the loop so bufferReversed goes up from 0 to the size and buffer goes from size down to zero (index locations), or you could have bufferReversed index be the size - the loop, because starting would be 0 (size - loop, with loop being the size).

so it would look like this:
bufferReversed[size-loop] = buffer[loop];

**7stud** · 06-26-2005

My way doesn't work--the last character doesn't change

Code:

//switching two numbers:

int a = 10;
int b  = 20;

Get a piece of paper and make two columns:

Code:

 a=          b=
----        ----

Start off by filling in the starting values for 'a' and 'b':

Code:

 a=          b=
----        ----
 10          20

Now, if you add this line:

Code:

//switching two numbers:

int a = 10;
int b  = 20;

a = b;

What does 'a' equal? Cross out the starting value for 'a', and write down the new value for 'a'.

Now, add this line:

Code:

//switching two numbers:

int a = 10;
int b  = 20;

a = b;
b = a;

What does b equal? Look at your paper. Cross out the old value for 'b', and write down the new value. What are the ending values for 'a' and 'b'? Why didn't the numbers get switched?

**tinkerbell20** · 06-27-2005

I see...It's seems as if I need a third variable. mmmm...... How do I do it with a loop?

**elad** · 06-27-2005

Well you're basically doing two set's of variable swaps, name[0] with name[4] and name[1] with name[3]. See if you can figure out how to swap one variable with another outside a loop, and then try to write the swap inside a loop so you can swap as many variables as you want.

**~~ILoveVectors~~** · 06-27-2005

Code:

#include <iostream.h> // I know it's the old method, but that's what's the book writes
rev(char name[6]);

main()
{
     char name[6];
     cout << "What is your first name (5 letters, please)? ";
     cin  >> name;

     rev(name);
     cout << "Your name spelled backwards is " << name << "\n";
     return 0;
}
//from here is what I added
rev(char name[6])
{
      char backup = name[0];
      name[0] = name[4];
      name[1] = name[3];
      name[3] = name[1];
      name[4] = name[0]; 
      name[4] = backup;
      return 0;
}

**sigfriedmcwild** · 06-27-2005

Originally Posted by ILoveVectors

Code:

#include <iostream.h> // I know it's the old method, but that's what's the book writes
rev(char name[6]);

main()
{
     char name[6];
     cout << "What is your first name (5 letters, please)? ";
     cin  >> name;

     rev(name);
     cout << "Your name spelled backwards is " << name << "\n";
     return 0;
}
//from here is what I added
rev(char name[6])
{
      char backup = name[0];
      name[0] = name[4];
      name[1] = name[3];
      name[3] = name[1];
      name[4] = name[0]; 
      name[4] = backup;
      return 0;
}

Check your code
This program is still buggy
name[1] is overwirtten by name[3] before it's copied.

Code:

rev(char name[6])
{
      char backup = name[0];
      name[0] = name[4];
      name[4] = backup;

      backup = name[1];
      name[1] = name[3];
      name[3] = backup;
 

      return 0;
}

This should work

**treenef** · 06-27-2005

Hi Tinkerbell,

Firstly, you are using deprecated headers.
It should be:

Code:

#include <iostream>
using namespace std;

If your teacher/lecturer tells you otherwise he needs to
be corrected. Why not be the one to correct him.

Secondly, you asked what is a loop?

A loop or "for loop" is vitally important in programming.
Let's say you wanted your program to count from 1 to 1000. Now you could do this:

Code:

cout<<1;
cout<<2;
cout<<3
.
.
.
cout<<1000;

This is obviously tedious? There is a much quicker way which involves using a for loop.

The way you write it is as follows:

Code:

for(int a=0; a<1000; a++)
{
cout<<a;
}

The important bits.
Now the "int a=0;" is your starting value.

The "a<1000" is your end value.

And the 'a++' tells you how much to add to the previous value. It is similar to saying a= a+1.

So if you wanted to count up in tens you would write:

Code:

for(int a=0; a<1000; a=a+10)
{
cout<<a;
}

So how does this help you with your example?
Well you can use the for loop as a pointer to the position in your array.

So how would you print out the contents of your array, from [0] to [5]?

for(int a=0; a<6; a++)
{
cout<<name[a];
}

Ok now all you have to do is figure out what you need to change to print out the array backwards. What would be the start value, the end value and how would the
a++ differ?

Have a go.

Once you've done that then read up on functions

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