Thread: increment char

Hi guys, i need some help with C functions, i'm looking for a way to do two things but i'm struggling a little, was wondering if someone here can point me in the right direction.

1st problem:
This is a trivial one i want to join some variables together to make a new one. i know in vb.net it would be somthing along the lines of:

Code:

 value3 = value1 & value2

so if value1 was "Hello" and value2 was "World" i then set a label.text to value3 it would read "HelloWorld", can i do this in C some how?

2nd problem:
This the code for my test app:

Code:

#include <stdio.h>
#include <stdlib.h>


int main()
{
 int node1 = 1;
 int node2 = 1;
 int node3 = 1;
 int node4 = 1;

        while (node4 <= 26){
        if (node1 <= 26){
        printf("%i:%i:%i:%i\n", node1, node2, node3, node4);

        node1 = node1++;
            }
            else if (node2 < 26){
                node1 = 1;
                node2 = node2++;
                }
                    else if (node3 < 26){
                    node1 = 1;
                    node2 = 1;
                    node3 = node3++;
                    }
                        else{
                        node1 = 1;
                        node2 = 1;
                        node3 = 1;
                        node4 = node4++;
                        }
        }
     return 0;
}

what i'm looking to do is output a string from "AAAA" to "ZZZZ", i have it working for "1:1:1:1" to "26:26:26:26" but am i able to change these numbers in to letters by doing something like this:

Code:

int letnum = 10;
char alphab = "ABCDEFGHIJLMNOPQRSTUVWXYZ";

/* then do somthing like the following */ 

char letter = left(alpha, letnum); 

/* to set "letter" to "J" */

Sorry if these are stupid questions, still very new to C.

Okiura

So do you have a C reference? If not, you should get one rather than asking every question you will ever have on a web forum.

In any event: 1) strcat, 2) use array indexing.

Originally Posted by Okiura

Hi guys, i need some help with C functions, i'm looking for a way to do two things but i'm struggling a little, was wondering if someone here can point me in the right direction.

1st problem:
This is a trivial one i want to join some variables together to make a new one. i know in vb.net it would be somthing along the lines of:

Code:

 value3 = value1 & value2

so if value1 was "Hello" and value2 was "World" i then set a label.text to value3 it would read "HelloWorld", can i do this in C some how?

No. Sorry, but it's that simple, you can't do that.

C is a language of numbers. It is only trivially aware of strings and text. If you want to manipulate lines (or pages) of text you need to use functions like those in the standard C string library. You would do well to familiarize yourself with these functions early on as you will likely spend most of your time working with them. The example above would be accomplished with the strcpy() and strcat() functions, like this...

Code:

char words[24];
char second[12];


// put text in char arrays
strcpy(words,"Hello ");
strcpy(second, "World!");

// join them
strcat(words, second);

printf("%s\n",words);

Yeah I know,that sucks ... but that's how it's done.

2nd problem:
This the code for my test app:

Code:

#include <stdio.h>
#include <stdlib.h>


int main()
{
 int node1 = 1;
 int node2 = 1;
 int node3 = 1;
 int node4 = 1;

        while (node4 <= 26){
        if (node1 <= 26){
        printf("%i:%i:%i:%i\n", node1, node2, node3, node4);

        node1 = node1++;
            }
            else if (node2 < 26){
                node1 = 1;
                node2 = node2++;
                }
                    else if (node3 < 26){
                    node1 = 1;
                    node2 = 1;
                    node3 = node3++;
                    }
                        else{
                        node1 = 1;
                        node2 = 1;
                        node3 = 1;
                        node4 = node4++;
                        }
        }
     return 0;
}

what i'm looking to do is output a string from "AAAA" to "ZZZZ", i have it working for "1:1:1:1" to "26:26:26:26" but am i able to change these numbers in to letters by doing something like this:

Code:

int letnum = 10;
char alphab = "ABCDEFGHIJLMNOPQRSTUVWXYZ";

/* then do somthing like the following */ 

char letter = left(alpha, letnum); 

/* to set "letter" to "J" */

Sorry if these are stupid questions, still very new to C.

Okiura

What you're looking for is the character's offset into the ascii code ... if you do this...

Code:

printf("%c %c %c %c", node1 + 'A', node2 + 'A', node3 + 'A', node4 + 'A');

You'll get characters instead of numbers on your screen...

Originally Posted by tabstop

So do you have a C reference? If not, you should get one rather than asking every question you will ever have on a web forum.

In any event: 1) strcat, 2) use array indexing.

yes i do, i have google too but was struggling to get a useful answer.


@CommonTater

thanks for you response thats exactly what i was looking for! made some changes and now my code does exactly what i want it too, also you explained in a way that was easy to follow

I don't know which compiler you're working with ... but it should have some kind of library documentation with it... You really should get yourself familiar with it's various functions. Also you would do yourself a favor by spending a bit of time with a good tutorial or book on C... It seems a simple language at first but even 8 years into it, it still surprises me from time to time... Read the pages, do the exercises, one by one. In the end you'll be glad you did.

Code:

node1 = node1++;

This code actually results in undefined behavior, and is thus not the same as node1++. You cannot modify something at the same time you're assigning to it.

This problem is not just theoretical. I have compilers that produce different results for the undefined code. Some perform an increment, some leave the value the same.

Good to know, if that's true.

Shouldn't it always work though?
It is a post increment, and should only and always occur after node1 is evaluated.
consider:
a = b++;

Should be well defined, a = b, then b is incremented.

So,

a = a++;

a = a, then a is incremented.

Originally Posted by megafiddle

Shouldn't it always work though?
It is a post increment, and should only and always occur after node1 is evaluated.
consider:
a = b++;

Should be well defined, a = b, then b is incremented.

So,

a = a++;

a = a, then a is incremented.

The quick and easy answer is that even if it appears to be well-defined, it explicitly is not:

Originally Posted by C99 6.5p2

Between the previous and next sequence point an object shall have its stored value modified at most once by the evaluation of an expression.

But I'll try to explain why there are multiple ways to reasonably interpret how the expression should be evaluated.

First, ask yourself why the post-increment should necessarily occur after the assignment. Post-increment yields the previous value and then increments the object; but when does that increment occur? Does it have to occur after all other parts of the expression have been evaluated? It does not. It just has to happen by the next sequence point, which in this case is the semicolon.

So take the expression a=a++, and let's see two ways it might be interpreted:

Code:

int tmp;
tmp = a; /* remember the previous value */
a = a + 1; /* perform the increment */
a = tmp; /* perform the assignment (using the stored value) */

How would this violate the rules of post-increment? It doesn't: the previous value is being used, the increment is happening, and the assignment is happening. Here's another way it could be done:

Code:

a = a; /* perform the assignment */
a = a + 1; /* perform the increment */

So the first bit of code keeps the old value of a, the second results in an increment.

There is nothing that guarantees that one part of the expression will happen before the other. You're given special guarantees at sequence points (these are, more or less, places that force evaluations to be completed), but there is no sequence point at = or ++.

Interesting. Thanks.

Where are the sequence points in

Code:

a = a++;

As cas said, there aren't any (except the semicolon at the end that completes the statement). The operations inside the statement can be performed in any order.

Got it.

I did point out that

Code:

node1 = node1++;

could be replaced with

Code:

node1++;

It should be mentioned to Okiura, that this not only true, but recommended.