The structure of C programs, continued
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
/* Compile this program with:
cc -std=c11 -Wall -Werror -o rotate rotate.c
*/
#define ROT 13
static char rotate(char c)
{
c = c + ROT;
.....
return c;
}
int main(int argcount, char *argvalue[])
{
// check the number of arguments
if(argcount != 2) {
....
exit(EXIT_FAILURE);
}
else {
....
exit(EXIT_SUCCESS);
}
return 0;
}
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Same program, but more to note:
- A variety of brackets are employed, in pairs,
to group together items to be considered in the same way.
Here:
- angle brackets enclose a filename in a
#include directive,
- round brackets group items in arithmetic expressions and function
calls,
- square brackets enclose the index when access arrays
(vectors and matrices...) of data, and
- curly brackets group together sequences of one or more
statements in C.
We term a group of statements a block of statements.
- Functions in C,
may be thought of as a block of statements to which we give a name.
In our example,
we have two functions - rotate() and main().
- When our programs are run by the operating system,
the operating system always starts our program from main().
Thus, every complete C program requires a main() function.
The operating system passes some special information to our main()
function, command-line arguments,
and main() needs a special syntax to receive these.
- Most C programs you read will name main()'s parameters
as argc and argv.
- When our program finishes its execution,
it returns some information to the operating system.
Our example here exits by announcing either its
failure or success.
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CITS2002 Systems Programming, Lecture 2, p2, 25th July 2023.
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CITS2002