Thread: General C questions

Originally Posted by bluej322

Hi, i have a few C questions that are nagging me:

1) Why don't I need to place a '&' before strings when using scanf()?

2) How can access individual characters in an integer? (e.g. - find the occurrences of 4 in the integer 142342)

3) How can I assign string to a variable after its initial declaration?
example -
when i try to compile:

char string[10] = "First";
string = "second";

i get:

test.c: In function ‘main’:
test.c:10: error: incompatible types in assignment

4) How can I blank out an element of an array? (e.g. - remove the 'b' in "qubestion")

5) Are there any GUI's for C?

I know i have a few more but I can't remember them at the moment. Thanks in advance.

1. Someone told me the array name is a pointer to the first element.

2. The itoa function takes an integer as input and returns a string.
itoa(3) - Linux man page

3. I've had trouble with that, too. When in doubt, use bzero and sprintf. Those usually work for me.
man page bzero section 3
sprintf(3): formatted output conversion - Linux man page

4. If that string were an array, you could assign the third element of that array to an invisible character, so users see "question", without the "b". Don't make it a null byte, though, that will cut the string short at "qu".

5. The X Window System and Apple's Carbon framework are to be used with C.

Originally Posted by bluej322

Hi, i have a few C questions that are nagging me:

1) Why don't I need to place a '&' before strings when using scanf()?

2) How can access individual characters in an integer? (e.g. - find the occurrences of 4 in the integer 142342)

3) How can I assign string to a variable after its initial declaration?
example -
when i try to compile:

char string[10] = "First";
string = "second";

i get:

test.c: In function ‘main’:
test.c:10: error: incompatible types in assignment

4) How can I blank out an element of an array? (e.g. - remove the 'b' in "qubestion")

5) Are there any GUI's for C?

I know i have a few more but I can't remember them at the moment. Thanks in advance.

1. When needed, the name of an array will degrade to a pointer to the first element.
2. Use sscanf to convert the integer to a string. Then you can access the indexes of the string with [].
3. You cannot reassign an array like that. You can reassign a pointer though:

Code:

const char* s = "first";
s = "second";

4. You can't. What you can do is use memmove() to move all the characters up one spot in the array (which will overwrite your unwanted character).
5. Yes, but this depends on the operating system you are targeting.

Oh yeah, and how can i run executable files with C?

The result of compiling the source file should be an executable file. Just run it as you would any other executable file.

Originally Posted by bluej322

Oh yeah, and how can i run executable files with C?

An executable is what your compiler outputs by default. If you compile this C program...

Code:

#include <stdio.h>

int main() {
    printf("hello world\n");
    return 0;
}

...using this command (assuming the source file's name is prog.c)...

Code:

cc prog.c

...your compiler will produce an executable file named a.out. On some operating systems, you can double-click on this executable, and the OS will open a terminal window. On Windows, the Command Prompt window will be open for a second; on Mac OS X, the Terminal.app window will stay open until you close it; on Ubuntu, it appears nothing happened.

To run your executable, type the following command.

Code:

./a.out

You should see "hello world" appear on the output. Of course, the compilation and execution method varies from operating system to operating system, from IDE to IDE.

For everyone here who thinks arrays are just pointers, go and read this -> Question 6.2

Then read the rest of section 6 of the CLC FAQ.