A C Program

Writing a program in C requires one additional step compared to that of Perl:

• Create a text file with the commands you wish to carry out,
• Compile this program to make an executable,
• Run the executable.

A simple C program that just prints out something to the terminal screen is

#include <stdio.h>

/* This is a comment */

int main(void) {
  printf("Hello\n");
  return 0;
}

After creating this file, save it as, for example, hello.c, and compile it as

  C:\> bcc32 hello.c
  C:\> hello

on Windows (using the Borland bcc32 compiler), or on Unix as

  bash$ gcc -o hello hello.c
  bash$ ./hello

The first stage of compiling the file creates the executable - on Windows, the name of the executable is, by default, hello.exe, while on Unix one specifies it with the -o option. The second stage runs this executable.

There are some notable differences between this file and the equivalent one as a Perl script:

• the notation for comments - in C, things between /* and */ are comments, even spanning multiple lines;
• the presence of the line #include <stdio.h> - this pulls in the header file stdio.h (standard input and output), which contains some common definitions (prototypes) for various functions;
• the presence of an int main(void) { ... } - this in the ``main'' routine, and contains the code to be run; the int signifies that this routine must return an integer (typically 0 if the program runs successfully, and non-zero if an error of some sort is encoutered);
• the use of printf (``print format''), rather than print, in printing to the terminal screen.