Software

Computer Languages

	program	number
		integer	i

		do 10 i=1,10
			print*, i
 10 		continue
		stop
	end

(defun number (n)
	(cond ((equal n 10) n)
	      (t (print n) (number (+ n 1)))))
(number 10)

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

int main () {
	int	i;

	for (i=1; i<=10; i++) printf ("%d\n", i);
	exit (0);
}

The C Language

#include <stdio.h>

int main () {
	printf ("Hello, World!\n");
	exit (0);
}

Elements of a C program:

• Comments, text beginning with /* and ending with */. Comments can appear before, after, or between any syntactic elements, and explain to the reader what is going on in the program. They are ignored by the compiler.
• Identifiers with names starting with alphabetic characters or the underscore (_) and containing alphabetic and numeric and _. Examples of identifiers: main, printf, x, sum123, this_is_an_identifier.
• Declarations of variables and functions.
• Functions, including exactly one function called "main", named using identifiers, returning some value, and contained in {}'s. For instance,

  int foo () { stuff }
  

• Statements contained in functions, either expressions or control statements.
• Variables, named with identifiers and given a type. declared with variable declaration statements. You must specify the type and name of a variable using a declaration statement, for example:

  	int	a;			/* a is an integer */
  	float	hello;			/* hello is a floating point number */
  	char	x, y;			/* x and y are single characters */
  

  The basic types are:
  • int: integer.
  • long: long integer (on our system, same as int).
  • float: floating point value, approximating real numbers.
  • double: higher precision version of float.
  • char: character (usually one byte).
  You can also make up your own types and have arrays (vectors) of the simple or made-up types.
• Constants:
  • Integer constants: in decimal e.g. 123, hexadecimal preceded by "0x", e.g. 0x12a, or octal preceded by "0", e.g. 0123.
  • Floating point: zero or more digits to the left and/or right of the decimal, e.g. 123.456. Also, exponential notation: e.g. 1.3e9 means 1.3 times 10 to the 9th power.
  • Character: a single character enclosed in single quotes, e.g. 'a'. Some special non-printing characters are represented preceded by a backslash, e.g. '\n' means newline (ASCII 10).
  • Character string: zero or more characters in a sequence, enclosed in double quotes, e.g. "Hello, World!\n"
• Preprocessor directives: Begin with # and tell the C preprocessor to do some action while compiling the program. For instance, #include tells the C compiler to include another file into the current file while compiling; this is how function declarations for things like printf are brought into your program.
• Expressions: Combination of constants, variables, operators, and function invokations that has a value. For example, a + b, 2 * 10.0, x + sqrt (y), etc.

#include <stdio.h>

int main () {
	float	num;

	num = 123;
	printf  ("%f squared is equal to %lf\n", num, num * num);
        return 0;
}

123.000000 squared is equal to 15129.000000

#include <stdio.h>

int main () {
	int	age;
	float	mhr, r1, r2;

	printf ("How old are you? ");
	scanf ("%d", &age);
	mhr = 220.0 - age;
	r1 = 0.65 * mhr;
	r2 = 0.80 * mhr;
	printf  ("Your heart rate should be"
		" between %0.2f and %0.2f during aerobic exercise\n", r1, r2);

        return 0;
}

Your heart rate should be between 130.00 and 160.00 during aerobic exercise

#include <stdio.h>

int main () {
        float   degrees, radians;

        printf ("Enter the angle in degrees: ");
        scanf ("%f", &degrees);
        radians = (degrees / 360.0) * 2 * 3.14159;
        printf ("%f degrees = %f radians.\n", degrees, radians);
        return 0;
}

#include <stdio.h>
#include <ctype.h>

int main () {
	char	in_char, up, lo;
	int	code;

	printf ("Enter a letter: ");
	scanf ("%c", &in_char);
	up = toupper (in_char);
	lo = tolower (in_char);
	printf ("lowercase is %c, uppercase is %c\n", lo, up);
	code = (int) in_char;
	printf ("ASCII code is %d\n", code);
	return 0;
}

Enter a letter: f
lowercase is f, uppercase is F
ASCII code is 102

#include <stdio.h>

int main () {
	int	a;

	printf ("Enter a number: ");
	scanf ("%d", &a);
	printf ("%d in hexadecimal is %x\n", a, a);
}

Enter a number: 31
31 in hexadecimal is 1f