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How do I create, compile, and run a C program?

- 1 -

At the command line, pick a directory to save you program to, and enter:

vi firstprog.c

Note:

All C source code files must have a .c file extension.

- 2 -

Enter the following program, then save and exit Vi:

#include <stdio.h>
int main()
{
	int n;
	for (n = 0; n < 7; n++)
		printf ("Hello, World!\n");
	return 0;
}

- 3 -

Enter:

gcc -o myprog firstprog.c

...to, using the GNU C Compiler (gcc), compile and output (-o) an executable file, called myprog, from the source code, firstprog.c.

- 4 -

To run the program, enter:

./myprog

Note:

To save you having to precede an executable with a ./ when running it from the current directory, add the following to your ~/.bash_profile file:

PATH=$PATH:./

---

Code example explained

Here's an explanation of the above program:

1	#include <stdio.h>	During compilation, include the header file stdio.h, located in the /usr/include directory, and required by the printf function call in line 6, so the program knows what printf does. Functions allow a program to be broken down into pieces, and called when required at points in a program. For details on stdio.h, enter: man stdio
2	int main()	Begin the main() function, a special function indicating where to begin the program when it's run.
3	{	The beginning brace, indicating the content's of the main() function featured in lines 4-7.
4	int n;	Declare the integer (whole-number) variable n. A variable being a placeholder for data. For example, n could store 42, or -253, but not x or 5.1. (For the latter two, you would use char n and float n, respectively.)
5	for (n = 0; n < 7; n++)	Begin a loop, causing the content of the loop (line 6) to repeat while the variable n is less-than 7 (n < 7). n begins at 0 (n = 0), and after each iteration of the loop (i.e. immediately after line 6), is incremented by 1 (n++).
6	printf ("Hello, World!\n");	Print to screen the string "Hello, World!". The \n (newline character) part causes the next thing to be printed to screen to start on a new line.
7	return 0;	Exit the main() function (and therefor the program), returning a 0, indicating success to the operating system. The presence of this line is why the int part features in line 2.
8	}	The ending brace, indicating where the function, in this case main(), ends.

It should be noted that library files (also known as header files) play a big part in C, allowing other functions to be built from C's small set of keywords (commands). C libraries are included in Linux by glibc, massively extending the commands at your disposal. Because most software (including Linux, the kernel) depend so much on GCC and glibc, as well as many other important GNU tools, many often refer to the operating system, as GNU/Linux, rather than just Linux. Glibc is fully ANSI compliant, an important standard, allowing code written for one compiler to work with another compliant compiler.

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