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Case study 1: Calculate the approximation of Pi

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Calculate the approximation of Pi by formula

 1 1 1 4 3 5 7

with error 1e-4.

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Algorithm 1. pi = 0, s = 1, n = 1, t = s/n 2. while fabs(t) > 1e-4 do 1. pi = pi + t 2. n = n +2 3. s = -s 4. t = s / n; 5. end while 3. Pi = 4 * pi

CP104 Introduction to Programming

Repetition and loop

Lecture 15 __ 1

Implementation

#include #include 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

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Calculate the first 40 number of Fibonacci sequence: F(1) = 1, F(2) = 1, …, F(n) = F(n-1) + F(n-2)

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Algorithm 1. f1 = 1, f2 = 1, i = 1 2. For i from 1 to 20 do 1.

2.

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Print f1 and f2 f1 = f1 + f2 f2 = f2 + f1 End of for loop

CP104 Introduction to Programming

Repetition and loop

Lecture 15 __ 3

Implementation

#include 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

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Problem: Convert a plain text to a cipher text by alphabet of module k. Where 0

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Encryption Algorithm: 1. Get a key k 2. While the input character c is not \n 3. Convert c into its cipher text by using the kth letter forward 4. End while Encryption Algorithm: 1. For key k 2. While the input character c is not \n 3. Convert c into its plain text by using the kth letter backward 4. End while

CP104 Introduction to Programming

Repetition and loop

Lecture 15 __ 5

Implementation

#include 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 /* 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