Case study 1: Calculate the approximation of Pi
•
Calculate the approximation of Pi by formula

1 1 1
 1     ...
4
3 5 7
with error 1e-4.
•
Algorithm
1. pi = 0, s = 1, n = 1, t = s/n
2. while fabs(t) > 1e-4 do
1.
2.
3.
4.
5.
pi = pi + t
n = n +2
s = -s
t = s / n;
end while
3. Pi = 4 * pi
CP104 Introduction to Programming
Repetition and loop
Lecture 15 __ 1
Implementation
#include <stdio.h>
#include <math.h>
main(){
int s = 1;
double n = 1, t = 1, pi = 0;
while (fabs(t)>= 1e-4)
{
pi = pi + t;
n += 2;
s = - s;
t = s/n;
}
pi = pi * 4;
printf("%10.6f\n", pi);
}
3.141393
CP104 Introduction to Programming
Repetition and loop
Lecture 15 __ 2
Case Study 2: Fibonacci Sequence
•
Calculate the first 40 number of Fibonacci
sequence:
F(1) = 1, F(2) = 1, …, F(n) = F(n-1) + F(n-2)
•
Algorithm
1. f1 = 1, f2 = 1, i = 1
2. For i from 1 to 20 do
1. Print f1 and f2
2. f1 = f1 + f2
3. f2 = f2 + f1
End of for loop
CP104 Introduction to Programming
Repetition and loop
Lecture 15 __ 3
Implementation
#include <stdio.h>
main(){
long int f1, f2;
int i;
f1 = 1;
f2 = 1;
for (i = 1; i<=20; i++)
{
printf("%12ld
%12ld ", f1, f2);
if(i%2==0) printf("\n");
f1 = f1 + f2;
f2 = f2 + f1;
}
}
CP104 Introduction to Programming
Repetition and loop
Lecture 15 __ 4
Case Study 3: Simple Encryption and Decryption
•
Problem:
Convert a plain text to a cipher text by alphabet of module k.
Where 0<k<26 is an integer, used a key to encode and decode.
For example if k = 3, A will be encrypted to D, and y will be
encrypted to b.
•
Encryption Algorithm:
1.
2.
3.
4.
•
Get a key k
While the input character c is not \n
Convert c into its cipher text by using the kth letter forward
End while
Encryption Algorithm:
1.
2.
3.
4.
For key k
While the input character c is not \n
Convert c into its plain text by using the kth letter backward
End while
CP104 Introduction to Programming
Repetition and loop
Lecture 15 __ 5
Implementation
#include <stdio.h>
main(){
char c;
int key;
printf("Input a key between 1 and 25: \n");
scanf("%d", &key);
while ((c = getchar())!='*')
{
if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z'))
{
c = c + key;
if (c > 'Z' && c <='Z'+key || c >'z')
c = c - 26;
}
printf("%c",c);
}
CP104 Introduction to Programming
Repetition and loop
Lecture 15 __ 6
Reading Data from a File
#include <stdio.h>
/* defines fopen, fclose, fscanf fprintf, and EOF
int
main(void)
{
FILE *inp;
/* input file pointer
*/
int sum = 0,
/* sum of scores input so far
score,
/* current score
*/
input_status; /* status value returned by fscanf
*/
*/
*/
inp = fopen("scores.dat", "r"); /* open a file for reading */
printf("Scores\n");
input_status = fscanf(inp, "%d", &score); /* read the first line from the file */
while (input_status != EOF) { /* if not the end of file sign */
printf("%5d\n", score);
sum += score;
input_status = fscanf(inp, "%d", &score); /* continue to read the next line */
}
printf("\nSum of exam scores is %d\n", sum);
fclose(inp); /* close the file */
}
Run by command line
CP104 Introduction to Programming
Repetition and loop
Lecture 15 __ 7
Structure Chart for Computing Solar Collecting Area Size
CP104 Introduction to Programming
Repetition and loop
Lecture 15 __ 8
Program to Approximate Solar Collecting Area Size
CP104 Introduction to Programming
Repetition and loop
Lecture 15 __ 9
Program to Approximate Solar Collecting Area Size (cont’d)
CP104 Introduction to Programming
Repetition and loop
Lecture 15 __ 10
Program to Approximate Solar Collecting Area Size (cont’d)
CP104 Introduction to Programming
Repetition and loop
Lecture 15 __ 11