Engineering H192 - Computer Programming
C Programming Basics
Lecture 5
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Lect 5
P. 1
Engineering H192 - Computer Programming
ENG H192 Course Web Page
• A web page which contains the course syllabus,
updated lecture notes and other useful
information may be found at:
http://feh.eng.ohio-state.edu
• A copy of Professor Dick Busick’s flowchart
spreadsheet is on the Web site
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Lect 5
P. 2
Engineering H192 - Computer Programming
C Program Basics
• C vs. C++
– C is a subset of C++. All of features in C are
contained in C++
– C++ adds more libraries with functions for
object oriented programming
– C++ also adds more keywords and some
added features.
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Lect 5
P. 3
Engineering H192 - Computer Programming
Keywords in C and C++
Certain words have a special meaning to the C or
C++ compiler. They are called reserved words or
keywords. We should not try to use these words as
names of variables or function names in a program.
The keyword list for C contains 32 words (see text,
pg. 44). C++ adds 30 more keywords (see text, pg.
563).
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Engineering H192 - Computer Programming
Some Keywords in C and C++
asm
auto
break
case
catch
char
class
const
continue
default
delete
do
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double
else
enum
extern
float
for
friend
goto
if
inline
int
long
new
operator
private
protected
public
register
return
short
signed
sizeof
static
struct
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switch
template
this
throw
try
typedef
union
unsigned
virtual
void
volatile
while
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P. 5
Engineering H192 - Computer Programming
Program Structure in C
• EACH complete C program is composed of:
–
–
–
–
–
Comment statements
Pre-processor directives
Declaration statements
One or more functions
Executable statements
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Engineering H192 - Computer Programming
Program Structure in C
• EACH complete C program is composed of:
– Comment statements
– Pre-processor directives
– Comment statements
– Declaration statements
– Comment statements
– One or more functions
– Comment statements
– Executable statements
– Comment statements
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Engineering H192 - Computer Programming
Comment Statements
• Formal Comments:
/* Comment ….. */
– Used for detailed description of functions or
operations (for our benefit, not compiler’s).
– Can take multiple lines in source file.
• Informal Comments (only in C++, not C):
// Comment ….. Ends at the end of line
– Used for quick comments like:
int temp; // temporary variable for storing
// the input value
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Engineering H192 - Computer Programming
Pre-Processor Directives
#include -- header files for library functions
Example:
#include <stdio.h>
Note Space
#define -- define constants and macros
Examples:
#define e 2.7182818
#define pi 3.14159265359
Note Spaces
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Engineering H192 - Computer Programming
Declarations
• Declarations tell the compiler what variable
names will be used and what type of data each
can handle (store).
• Example declarations:
int a, b, c ;
float r, p, q ;
double x, y, z ;
char m, n ;
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Engineering H192 - Computer Programming
Data Types
• Integer variables:
int a, b ;
• Integer variables, like a or b, store only whole
numbers like 3 or 7, not 3.33 or 7.65, and only up
to certain maximum values.
• Floating point variables:
float c, d ;
• Floating point variables, like c or d, store rational
numbers, like 3.14159, but only a limited number
of digits of precision.
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Engineering H192 - Computer Programming
Internal Storage Representation
• Definitions:
– Binary digit -- or a "bit", is either a 0 or a 1
– Byte -- usually a collection of 8 bits together
– Word -- often a collection of 4 bytes together
• On the SGI Unix system:
– an "int" data type takes up 4 bytes
(on some systems, an "int" is only 2 bytes)
– a "float" data type takes up 4 bytes
– a "double" data type take up 8 bytes
– a "char" data type takes up 1 byte
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Engineering H192 - Computer Programming
Programs Have One or More Functions
• Even the main program is a function.
The body of each user-written function is
enclosed in braces, { } (or curly brackets)
• The syntax of a function is:
<function type> function_name (arg. list)
{
/* beginning of function */
}
/* end of function
*/
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Engineering H192 - Computer Programming
Executable Statements
• Simple
Declaring variables
int temp ;
char a ;
Assigning Values
temp = 5 ; temp is assigned the value of 5
• Complex, i.e., Calling Functions
plotxy (x, y) ;
• Calculations
x = (5. / 2 + 6) * 7 ;
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Engineering H192 - Computer Programming
Arithmetic Operators
*
/
%
multiply
+
add
divide
subtract
remainder, where:
x = 13 % 5 ;
/* x will be equal to 3 */
• An expression can be used almost anywhere a
variable of the same type can be used.
Ex. expressions:
num + 3, a * d - 5, ...
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Engineering H192 - Computer Programming
Arithmetic Operators – Order of Evaluation
1. Parentheses: () – Evaluate from the inside out
2. Multiplication, Division, and Remainder:
*, /, and %
3. Addition and Subtraction:
+ and NOTE: Multiple occurrences of operations with the same
precedence evaluate from left to right. (D&D text, pg. 38)
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Engineering H192 - Computer Programming
Arithmetic Operators – Order of Evaluation
For example:
x = 2 * 3 - (4 + 5) + 8 % 7;
x
x
x
x
x
=
=
=
=
=
2 * 3 - 9 + 8 % 7;
6 - 9 + 8 % 7;
6 - 9 + 1;
-3 + 1;
-2;
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Engineering H192 - Computer Programming
Arithmetic Operators – Order of Evaluation
Another example:
x = 6 / 2 + 1 - 3 + 8 * 4;
x = 33;
x = 6 / (2 + 1) - (3 + 8) * 4;
x = -42;
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Engineering H192 - Computer Programming
Mixed Mode Arithmetic
• When performing arithmetic operations, the
"mode" will one of:
– Floating point, if both operands are floating
point
– Integer, if both operands are integer
– Mixed, if one operand in integer and the other
is floating point -- the result is floating point
• Integer operations produce integer results
(remember how you first learned to to division?)
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Engineering H192 - Computer Programming
Assignment Operators
Operator:
=
+=
–=
/=
*=
%=
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Example:
Meaning:
x=5;
x += 5 ;
x –= 5 ;
x /= 5 ;
x *= 5 ;
x %= 5;
x=5;
x=x+5;
x=x–5;
x=x/5;
x=x*5;
x= x%5;
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Engineering H192 - Computer Programming
Assignment Operators
Example of assignment operators:
int a = 4, b = 2, c = 36 ;
a += b ;
/* This adds b to a, a = ?
c /= a + b ;
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*/
/* What is value of c now? */
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Engineering H192 - Computer Programming
Assignment Operators
Example of assignment operators:
int a = 4, b = 2, c = 36 ;
a += b ;
/* This adds b to a, a = ?
*/
[ Answer: a = a + b, so a = 4 + 2 or a = 6 ]
c /= a + b ;
/* What is value of c now? */
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Engineering H192 - Computer Programming
Assignment Operators
Example of assignment operators:
int a = 4, b = 2, c = 36 ;
a += b ;
/* This adds b to a, a = ?
*/
[ Answer: a = a + b, so a = 4 + 2 or a = 6 ]
c /= a + b ;
/* What is value of c now? */
[ Answer: c = c / (a + b), and a = 6 now,
so c = 36 / (6 + 2), so c = 36 / 8 or c = 4 ]
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Engineering H192 - Computer Programming
Increment/Decrement Operators
Operator:
count++ ;
++count ;
count-- ;
--count ;
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Meaning:
count = count + 1 ;
count = count + 1 ;
count = count - 1 ;
count = count - 1 ;
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When?
After use
Before use
After use
Before use
Lect 5
P. 24
Engineering H192 - Computer Programming
Increment/Decrement Operators
Examples of increment and decrement operators:
int a = 4, b = 2, c;
c = ++a + b-- ;
/* What are the values of a, b, c now?
*/
c = b-- - ++a ;
/* What are the values of a, b, c now?
*/
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Lect 5
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Engineering H192 - Computer Programming
Increment/Decrement Operators
Examples of increment and decrement operators:
int a = 4, b = 2, c;
c = ++a + b-- ;
/* What are the values of a, b, c now? */
(Answers: a = 5, b = 1, c = 7)
c = b-- - ++a ;
/* What are the values of a, b, c now?
*/
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Lect 5
P. 26
Engineering H192 - Computer Programming
Increment/Decrement Operators
Examples of increment and decrement operators:
int a = 4, b = 2, c;
c = ++a + b-- ;
/* What are the values of a, b, c now? */
(Answers: a = 5, b = 1, c = 7)
c = b-- - ++a ;
/* What are the values of a, b, c now?
*/
(Answers: a = 6, b = 0, c = -5)
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Engineering H192 - Computer Programming
Relational Operators
Operator:
<
>
<=
>=
==
!=
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Meaning:
Less Than
Greater Than
Less Than or Equal To
Greater Than or Equal To
Exactly Equal To
Not Equal To
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Engineering H192 - Computer Programming
Relational Operators
• Used for asking questions like:
Is x bigger than 10?
• In C, the value of 1 stands for true and 0 stands
for false. But C will recognize any non zero value
as true.
• NOTE:
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"==" is NOT same as "="
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Engineering H192 - Computer Programming
Logical Operators
! (not)
Ex: a != b is true if a and b are not equal
&& (and)
Ex: 5<6 && 7>4 is true, but
5>6 && 7>4 is not true (i.e., false)
|| (or)
Ex: 5>6 || 7>4 is true
5<6 || 7<4 is also true
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Engineering H192 - Computer Programming
Exponentiation Operations
Exponentiation is not written as x**2 or x^2
C does not have an exponentiation operator. You
can use the math function pow (a, b) which
raises a to the b power. You must put a #include
<math.h> in your source code and must also use
the -lm switch in your compile command when on
the SGI UNIX system.
Ex:
>g++ -o myprog.out myprog.cpp
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Engineering H192 - Computer Programming
Skeleton Program
/*****************************************/
/* Name: Brutus Buckeye
*/
/* Seat No. 0, Instr: W. Hayes
*/
/* Program progname/assignment */
/*****************************************/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main ( )
{
statements ;
}
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Engineering H192 - Computer Programming
Shell for programs
• Create a “skelton.cpp” file as a basis for your
assignments
• Going to look much like Skeleton program on
previous slide
• USAGE for an program
– Open skelton.cpp
– Save to name for program
– Edit program
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Engineering H192 - Computer Programming
Today’s Assignment
• Today’s Assignment is G04
• G03 has a C program that calculates values and
assigns them to variables.
• You are to do the calculations by hand (quiz and
midterm material!!) and print the answers on the
problem sheet.
• Then, copy the program into your account and
run it to get the correct answers. Compare your
hand calculations to the computer’s calculations.
• What needs to be added to the code so that you
know what the computer calculated?
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