The Basics of C - Math Functions and characters

C Programming
a Q & A Approach
by H.H. Tan, T.B. D’Orazio, S.H. Or & Marian M.Y. Choy
Chapter 3
The Basics of C – Math Functions and
Character File Input/Output

4
Programming Example
 Calculate the surface area of a triangle
 the length of the two sizes
 the angle between the two sizes
 all data are input from user
 Procedure of the program
 figure out the right formula:
 define the right data type
 convert the formula to C expression
 output the results

1
l
2
l
1 2
0.5 sin( )
S l l 


Step1:Flow chart
Introduction to Programming in C 5

Step2:create a project.
 1.create a folder:
 2.create a project.

Step3:create a program
structure ,compile and run

Step4:Declare the variables:
length1,length2,angle,area

Step5:Input values for:
length1,length2,angle

Step6:calculation

Step6:Display result
Test Running result:
Please input length1:
5
Please input length2:
8
Please input angle:
90
The area of this triangle is:20.000000

12
Use of Double
 Double can carry a large number of digits
 important when doing a large number of
calculations
 more memory is required
 e.g. computing 100
 With 5 significant figures
(3.1416)100
= 5.189061599 * 1049
 Using 8 significant digits
(3.1415926)100
= 5.1897839464 * 1049
 Accuracy is reduced after numerous arithmetic
operations

13
Item float double long double
Memory
used
4 bytes = 32 bits 8 bytes = 64 bits 10 bytes = 80
bits
Range of
values
1.1754944E - 38 to
3.4028235E + 38
2.2250738E - 308
to 1.7976935E +
308
Approximately
1.0E - 4931
to 1.0E +
4932
Precision 6 15 19
printf
format
%f, %e, %E, %g,
%G
%lf, %e, %E, %g,
%G
%Lf, %Le,
%LE, %Lg,
%LG

Example for %g %f %e
Memory
Errors

15
C Mathematical Library Functions
 Input argument(s) x or y and return
values are of double type
 argument be in radians, not degrees
FUNCTION NAME CALCULATING
sin(x) sine of x, x is in radians
exp(x) natural exponential of x
log(x) natural logarithm of x
sqrt(x) square root of x
pow(x, y) x raised to the power of y

17
Function
name
Example Description
abs(x) y=abs(x); absolute value of an int type argument, x and y
are of type int (Note: needs #include
<stdlib.h> not math.h)
fabs(x) y=fabs(x); absolute value of a double type argument, x and
y are of type double (Note: needs #include
<stdlib.h> not math.h)
sin(x) y=sin(x); sine of an angle in radians, x and y are of type
double
cos(x) y=cos(x); cosine of an angle in radians, x and y are of type
double
tan(x) y=tan(x); tangent of an angle in radians, x and y are of
type double
log(x) y=log(x); natural logarithm of x, x and y are of type double
log10(x) y=log10(x)
;
logarithm to the base 10 of x, x and y are of type
double

18
3.2 Single Character Data
 Character type, char, refers to more than
just lowercase and uppercase letters
 Graphic characters such as !, #, and ^.
 Escape sequences (like n and r) also are
regarded as single characters

20
Character
 Declared with
char variable1, variable2, variable3, . . .;
 e.g.
char c1, c2, c3, c4, c5, c6, c7,
c8, c9, c10, c11;
 Assignment of char
enclose the value(constant) in single quotes, ‘
‘, e.g. c1 = 'g';

21
Character Processing
 C regards escape sequences as a single
character, e.g.
c3 = 'n';
 To print characters
printf ("%c %c n", c1, c2);
 C treats characters with their integer values
printf ("n%d %dn", c4, c5);
 If c4, c5 were input as ‘x’ and ‘p’, the ASCII
values 120 and 112, are printed

22
Read Characters from Keyboard
 Using the scanf with %c
scanf ("%c%c", &c4, &c5);
We can not get space, Enter … white-space
characters from keyboard

23
Ο scanf function classifies what is in the
format string into three categories:
1. Conversion / format specifiers (begins with a
%)
2. White-space characters (which for scanf is
not just a space, scanf treats Tab, and Enter
[newline n] also as white spaces)
3. Non-white-space characters

24
Ο When scanf has a space in its string literal, that space causes
scanf to skip over one or more white-space characters in the
input buffer to get to the next non-white-space character
Ο when reading characters, must make sure no white space in
string literal for scanf
● For example,
scanf ("%c%c", &c1, &c2);
will not accept

as input!

25
getche
 Form
char c3=getche();
 Deals directly with the operating system
 Does not require Enter key to be pressed
 Similar functions to input a char:
getch getchar

Homework 5
 Make a program or programs to input a
char with:
scanf
getch
getche
getchar
 Draw a conclusion after compare the
difference of four functions in running
results.

27
3.3 File Processing
 Typical file processing procedures:
Opening a file
• When program is being executed, it will
search for a file with that name
Reading/writing data from a file
• Read using the fscanf( ) function
• Write using the fprintf()
Close the file

28
//varialbes
double xx ;
int ii, kk;
FILE *fp;
//open file
fp = fopen ("AB.txt","r");
//input from file
fscanf (fp,"%d",&ii);
fscanf (fp,"%d%lf",&kk,&xx);
//close file
fclose (fp);
//display on the screen.
printf ("ii=%5dnkk=%5dnxx=%9.3lfn",ii,
kk, xx);
36
123 456.78
Output
Input file AB.txt

Files in project
Data file
Source code file
Project file
Executable file

30
File Pointers
 Pointer variables holding address to the file
FILE *inptr;
inptr is the file pointer
 FILE is a derived data type defined in stdio.h
 Use fopen to create a link between a disk file and a file pointer, thus
accessing the file content
file_pointer = fopen (file_name, access_mode);
 e.g.
inptr = fopen (“C3_4.IN","r");
 file_name and the access_mode are in string literals
 “c3_4.in” is the actual disk file name to be opened
 The file pointer being received is then used to handle the actual file
 “r” means that we want to read data, i.e., read mode access
 Use “w” for write access

FILE *fopen(const char
*filename, const char *mode)
Sr.No. Mode & Description
1
"r"
Opens a file for reading. The file must exist.
2
"w"
Creates an empty file for writing. If a file with the same name already
exists, its content is erased and the file is considered as a new
empty file.
3
"a"
Appends to a file. Writing operations, append data at the end of the
file. The file is created if it does not exist.
4
"r+"
Opens a file to update both reading and writing. The file must exist.
5
"w+"
Creates an empty file for both reading and writing.
6
"a+"
Opens a file for reading and appending.
31

32
File Processing
 Use fscanf() to read data from a file
fscanf(file_pointer, format_string,
argument_list);
 Reads the contents of the file indicated by file_pointer according
to the conversion specifications in format_string.
 Basically similar to that of scanf, only that the content is now
being read from the file, e.g.
fscanf(inptr, "%d %lf",&kk,&xx);
 Although C will automatically close all open files after execution,
it is still recommended to close a file manually, using the fclose()
fclose(file_pointer);
example
fclose(inptr);

Example for inputting from file

34
3.4 Writing Output to a File
double income=123.45, expenses=987.65;
int week=7, year=2006;
FILE *myfile;
myfile = fopen ("L3_5.OUT","w");
fprintf (myfile,"Week=%5dnYear=%5dn",week,year);
fprintf (myfile,"Income =%7.2lfn Expenses=%8.3lf
n",
income,expenses);
fclose (myfile);
Output file

Files in the project
Before
execution
After
execution

36
File Processing
 Use the fprintf() function to write data to a file.
fprintf(file_pointer, format_string, argument_list);
example
fprintf(myfile," Week = %5dn Year = %5dn",week, year);
 Note we use the mode string “w” here for write
access

Example for outputting from file
v

38
3.5 Applications -Example 1
7.0
5.0
l1
h1
l2
h2
h3
l3
We have four right triangles, the vertical length of the next triangle is half of the
previous one; the horizontal length of the next triangle is incremented 1 from the
previous one. Initially, the vertical and horizontal length of the first right triangle is
7.0 and 5.0. You are asked to write a program to calculate the dimension of each
triangle and their surface area.

39
 Program developing procedure
Begin // include some preprocessing directives, stdio.h, math.h, etc
Declare variables //choose right variable names and data types
initialize horizontal leg length of the first triangle // can be done during declaration
initialize vertical leg length of the first triangle
Calculate area of first triangle // convert math expression to C
Calculate horizontal/vertical leg lengths of second triangle // using correct C operators
Calculate area of second triangle
Calculate horizontal /vertical leg lengths of third triangle
Calculate area of third triangle
Calculate horizontal /vertical leg lengths of fourth triangle
Calculate area of fourth triangle
Print results onto the screen /file
End // does the program need to return some value
3.5 Applications

40
#include<stdio.h>
void main(void)
{
double horiz_leg, vert_leg, area1,area2,area3,area4;
horiz_leg = 5.0;
vert_leg = 7.0;
area1 = horiz_leg * vert_leg * 0.50;
horiz_leg += 1.0;
vert_leg /= 2.0;
horiz_leg += 1.0;
vert_leg /= 2.0;
horiz_leg += 1.0;
vert_leg /= 2.0;
printf("nn"
"First triangle area t= %6.2f n"
"Second triangle area t= %6.2f n"
"Third triangle area t= %6.2f n"
"Fourth triangle area t= %6.2f n",area1,area2,area3,area4);
}
How to modify the
code in order to print
the results onto a file
too?

41
Assume that one person can push with the force of f=0.8kN
and that we have a car of m=1000kg. Write a program to
calculate the final velocity of the car by taking values of
number of people pushing the car and the distance they
pushed.
 Figure out the right formula to get the final velocity
 Determine the origin of the required information
number of people n <= input
distance s <= input
 Define variables
 read values for f,m from file1 on disk
 read values for n,s from user( keyboard)
 Calculate the results for v
 Display the values on window and save the values in file2 on disk
3.5 Applications - Exampel2
2
2
1
mv
Fs  m
Fs
v /
2

n
F f


42
Key Points (Home work)
 math.h should be included
 declare right type for different variables
distance => float or double
people => integer
velocity => float or double
 using scanf to get values from user, fscanf to get values from
file
give information on what the user should provide
variable address operator &
 Output all of the values and results with printf on window, and
save all of the values and results with fprintf in file.
3.4 Applications - Exampel2

Homework-5
 Study the source code for
Applications -Example 1
 Finish Applications - Exampel2
Submit the source code as *.c or
*.cpp
Submit the snapshot of the
running window
Submit the input file and output
files

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