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Dec 28th, 2008

How to merge 2 strings ?

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Hi.

I am trying to merge 2 chars. in C but i don't know how to do it.

My code:

C Syntax (Toggle Plain Text)
char dd[1], aa[2];
 
dd[0] = "2";
dd[1] = "3";
 
aa[] = dd[0] + dd[1];
char dd[1], aa[2];

dd[0] = "2";
dd[1] = "3";

aa[] = dd[0] + dd[1];

So it aa[] should show: 23 but it gives error. Maybe i am doing it wrong. Please help. Also this is just demo code, i am actually inputting the values of dd[0] and dd[1] from user using getche() function

Thanks.

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kikloo

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Dec 28th, 2008

Re: How to merge 2 strings ?

Quote ...

char dd[1];

That's wrong. You're allocating memory for only one character. Should be dd[2].

Quote ...

aa[] = dd[0] + dd[1];

This statement adds the ASCII values of '2' and '3'. So your result will be 50(ASCII value of 2) + 51(ASCII value of 3). And the result can't be just assigned to an entire array.

If you just wanna merge two chars, you can use:

C Syntax (Toggle Plain Text)
aa[0] = dd[0];
aa[1] = dd[1];
aa[0] = dd[0];
aa[1] = dd[1];

But I'm not sure if that's what you're looking for. Maybe more info about what you're trying to do would help.

devnar

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Dec 28th, 2008

Re: How to merge 2 strings ?

You use the standard C functions strcat()

Last edited by Aia; Dec 28th, 2008 at 2:57 pm. Reason: Wrong function link

Aia

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Dec 28th, 2008

Re: How to merge 2 strings ?

Hi,

I am using a custom function in which I have made so that the user can input only 1 char. and that is also just a numeric char. so meaning that user can only enter from 0 to 9.

I am doing like following:

C Syntax (Toggle Plain Text)
char dd[2];
 
dd[0] = getinp(); // say user enetered 2
dd[1] = getinp(); // say user enetered 3
char dd[2];

dd[0] = getinp(); // say user enetered 2
dd[1] = getinp(); // say user enetered 3

Now I have to merge the both values so that it becomes 23 and I can check whether the value is less than 30 or not. How to achieve this ?

If i could just do the following:

C Syntax (Toggle Plain Text)
aa = dd[0] + dd[1]; // aa will then have 23
if (aa > 30)
{
printf ("Value should not be more than 30");
}
else
{
printf ("Thanks");
}
aa = dd[0] + dd[1]; // aa will then have 23
if (aa > 30)
{
printf ("Value should not be more than 30");
}
else
{
printf ("Thanks");
}

This is really what I am trying to do.

I am using a custom function becuase it does'nt allows a user to enter anything else other than numbers.

Thanks

kikloo

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Dec 28th, 2008

Re: How to merge 2 strings ?

If dd[0] and dd[1] contain the character they entered, the character is NOT the numeric value. (For example in ASCII '0' is 48)

So if the example is dd[0] = '2' and dd[1] = '3' then aa = dd[0] + dd[1]; would give aa the value 50 + 51 or 101.

If you want the numeric value I usually do something like (dd[0] - '0') which in our case would be 2.

So if we did that as we went, we could write

c Syntax (Toggle Plain Text)
aa = (dd[0] - '0') + (dd[1] - '0')
aa = (dd[0] - '0') + (dd[1] - '0')

There, now aa is 2 + 3 which makes aa 5. (wait, didn't you say it should be 23? maybe I missed something.)

I guess I could have done:

c Syntax (Toggle Plain Text)
aa = 10 * (dd[0] - '0') + (dd[1] - '0')
aa = 10 * (dd[0] - '0') + (dd[1] - '0')

That would be 23.

You could probably even do it without the array of characters (unless you needed them for something else):

c Syntax (Toggle Plain Text)
aa = (getinp() - '0');
aa = 10 * aa + (getinp() - '0');
aa = (getinp() - '0');
aa = 10 * aa + (getinp() - '0');

Last edited by Murtan; Dec 28th, 2008 at 3:20 pm.

Murtan

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Dec 28th, 2008

Re: How to merge 2 strings ?

Hi,

When I added the line:

C Syntax (Toggle Plain Text)
aa = 10 * (dd[0] - '0') + (dd[1] - '0');
aa = 10 * (dd[0] - '0') + (dd[1] - '0');

It gives me error:
Lvalue required

What does that means ?

Thanks.

kikloo

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Dec 28th, 2008

Re: How to merge 2 strings ?

c Syntax (Toggle Plain Text)
char onetwo[3]; /* for one, two, zero chars */
char one, two;
one = getche();
two = getche();
onetwo[0] = one; /* array indicies started from 0 */
onetwo[1] = two;
onetwo[2] = '\0'; /* c-string terminated zero byte */
/* Now you have well-formed c-string */
printf("echo: %s\n",onetwo);
char onetwo[3]; /* for one, two, zero chars */
char one, two;
one = getche();
two = getche();
onetwo[0] = one; /* array indicies started from 0 */
onetwo[1] = two;
onetwo[2] = '\0'; /* c-string terminated zero byte */
/* Now you have well-formed c-string */
printf("echo: %s\n",onetwo);

Remember: a single char is not a string in C, a c-string is an array of chars with zero byte at the end of its contents.

Last edited by ArkM; Dec 28th, 2008 at 3:30 pm.

ArkM

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Dec 28th, 2008

Re: How to merge 2 strings ?

HI,

I still don't get it. Please help me merge the string or chars. so that I can go ahead with the program

I am a php and VB programmer and its very easy to do this task in those languages.

VB: a = a & b
php: a = a . b;

What the syntax to do it in C ?

Arrrgh.

kikloo

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Dec 28th, 2008

Re: How to merge 2 strings ?

Your original program declared aa as an array of characters:

c Syntax (Toggle Plain Text)
char dd[1], aa[2];
char dd[1], aa[2];

In your most recent post, you treated aa as an integer:

c Syntax (Toggle Plain Text)
aa = dd[0] + dd[1]; // aa will then have 23
if (aa > 30)
aa = dd[0] + dd[1]; // aa will then have 23
if (aa > 30)

So I did too. It is not permitted to assign to the array.

Change your declaration to:

c Syntax (Toggle Plain Text)
char dd[2];
int aa;
char dd[2];
int aa;

Murtan

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Dec 28th, 2008

Re: How to merge 2 strings ?

>What does that means ?
It means you need to learn a little be more about array of chars and what they represent.
As far as the compiler is concerned aa is not a proper variable to re-assign the kind effect resulted from 10 * (dd[0] - '0') + (dd[1] - '0')

Click to Expand / Collapse Quote originally posted by ArkM ...

one = getche();
two = getche();

No reason to use a non-portable function when getchar() could have do.

Last edited by Aia; Dec 28th, 2008 at 3:50 pm.

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