Using variables
The Program
<![CDATA[
/* File: wreck.c
-----------------
Author: Sue Bogar
Date written: 9/2/95
A program that prints the depth of the wreck of the Hesperus
using 3 different units of measure: fathoms, feet, and inches.
*/
#include <stdio.h>
main()
{
/* Declare variables */
int inches, feet, fathoms;
/* Assign fathoms the depth of the wreck */
fathoms = 7;
/* Do conversions into feet or inches */
feet = 6 * fathoms;
inches = 12 * feet;
/* Print out the depths */
printf ("\nIts depth at sea: \n");
printf (" %d fathoms \n", fathoms);
printf (" %d feet \n", feet);
printf (" %d inches \n", inches);
}
]]>
The Output
<![CDATA[
lassie% cc wreck.c
lassie% a.out
Its depth at sea:
7 fathoms
42 feet
504 inches
]]>
Declaring variables
At the line:
int inches, feet, fathoms;
3 blocks of memory are allocated, each big enough to hold an integer.
The name inches is associated with the first block, feet the second and
fathoms the third. The blocks of memory contain garbage and will contain
grabage until you change the value of the variable.
Basic Data Types
Predefined types in C:
- Integer types (int, long int and short int)
- Floating point types (float and double)
- Character type (char)
Constants
Examples of integer constants
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0
77
]]>
These are not good integer constants
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1234567890 /* Legal, but might be too large */
0123 /* Legal, but in octal (base 8) */
123.0 /* A floating point constant */
]]>
What is an "integer expression"?
An "expression" is either a constant, variable, or the result
of operators involving expressions. So, an integer expression is an integer
constant, an integer variable, or the result of an integer-producing set
of operations on expressions.
Examples of floating point constants
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3.14159
314.159e-2
]]>
These are not good floating point constants
<![CDATA[
3,141.59 /* No commas allowed */
314159 /* This is an integer constant */
]]>
Examples of character constants
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'a'
'3'
]]>
Examples of string constants
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"Hello World"
"Charlie Brown and Snoopy"
"" /* the empty string */
" " /* string of spaces */
/* "This is a comment" */
]]>
An example showing assignment to different data types
The Program
<![CDATA[
/*
File: example.c
Assigning constants to different data types.
*/
#include <stdio.h>
main()
{
/*Declare variables */
int i;
double x;
char c;
/* Assign values to a variable of type int */
/* and print them */
i = 345;
printf("The variable i contains: %d\n", i);
i = 678;
printf("The variable i contains: %d\n", i);
i = 123.74;
printf("The variable i contains: %d\n\n", i);
/* Assign a value to a variable of type */
/* double and print it */
x = 314.159e-2;
printf("The variable x contains: %f\n", x);
x = 12;
printf("The variable x contains: %f\n\n", x);
/* Assign a value to a variable of type */
/* char and print it */
c = 'a';
printf("The variable c is %c character.\n", c);
}
]]>
The Output
<![CDATA[
lassie% cc example.c
lassie% a.out
The variable i contains: 345
The variable i contains: 678
The variable i contains: 123
The variable x contains: 3.141590
The variable x contains: 12.000000
The variable c is a character.
lassie%
]]>