Workshop03.docx lap trinh C cho người mới bắt đầu

Subject: PRF192- PFC
Workshop 03
Objectives:
(1) Practicing skills at analyzing and implementing programs using user-defined
functions.
(2)Making familiar with some basic algorithms
Grading 10 programs, 1 mark/program
Program 1:
Objectives Practice implementing simple functions
Related
knowledge
Definition: A prime is positive integer that is greater than 1 and it is the
multiple of 1 and itself only.
Theorem: The integer n is a prime if and only if n>1 and it can not be
divided by all integers from 2 to  square root of n .
Use the library math.h to get the function sqrt(double) for getting the
square root of a positive number.
Problem Write a C that will accept a positive integer n, n>=2 then print out primes
between 2 and n.
Analysis
Nouns:
positive integer
 int n
Suggested algorithm (logical order of verbs)
Begin
Do {
Accept n;
}
While ( n<2);
For ( i=2 to n )
If (i is a prime ) Print out i;  Function int prime (int i)
End
Algorithm for
checking
whether an
integer is a
prime or not
int prime( int n ) {
int m = sqrt(n); /* m: square root of n */
int i; /* variable having value from 2 to m */
if (n<2) return 0; /* Condition 1 is not satisfied */
for ( i=2; i<=m; i++) /* checking the second condition */
if (n%i==0) return 0 ; /* n is divided by i  n is not a prime */
return 1; /* n is a prime */
}
Program 2:
Related knowledge Leap year (y): (y%400==0 || ( y%4==0 && y%100!=0))
Problem Write a C program that will accept data of a day then print out
whether they are valid or not.
Analysis
Data of a day
Begin

 int d, m, y Accept d, m, y
If (valid(d,m,y)) print out “valid date”
Else print out “invalid date”
End
Algorithm for
checking whether a
date is valid or not
int validDate ( int d, int m, int y) {
int maxd = 31; /*max day of months 1, 3, 5, 7, 8, 10, 12 */
/* basic checking */
if ( d<1 || d>31 || m<1 || m>12) return 0;
/* update maxd of a month */
if ( m==4 || m==6 || m==9 || m=11) maxd=30;
else if (m==2) {
/* leap year? */
if ( y%400==0 || ( y%4==0 && y%100!=0) maxd=29;
else maxd=28;
}
return d<=maxd;
}
Program 3:
Related knowledge A point p is in a circle if the distance from the center to p is less than
the radius.
Problem Write a C program that will accept a point and a circle having the
center is (0,0) then print out the relative position of this point with the
circle.
Analysis
Nouns:
A point  double x,y
A circle  double r
Relative position
 int result
 -1: (x,y) is out of
the circle
 0: (x,y) is on the
circle
 1: (x,y) is in the
circle
Begin
Accept x, y;
Do {
Accept r;
}
While(r<0);
result = getRelPos(x,y,r);
if (result ==1) Print out “The point is in the circle”;
else if (result==0) Print out “The point is on the circle”;
else Print out “The point is out of the circle”;
End
Algorithm for
getting relative
position of a point
with a circle
int getRelPos ( double x, double y, double r) {
double d2=x*x + y*y; /* d2
= x2
+ y2
*/
double r2= r*r; /* r2
*/
if (d2<r2) return 1 ; /* d2
<r2
the point is in the circle */
else if (d2==r2) return 0 ; /* d2
=r2
the point is on the circle */
return -1 ; /* d2
> r2
the point is out of the circle */
}
Program 4:

Related knowledge n! = 1*2*3*…*n
Problem Write a C program that will accept a positive integer then print out its
factorial.
Analysis
A positive integer
 int n
Begin
Do {
Accept n;
}
While (n<0);
Print out factorial(n);
End.
Algorithm for
Computing factorial
of an integer
double factorial ( int n) {
double p=1;
int i;
for (i=2; i<=n; i++) p *= i;
return p;
}
Program 5:
Related knowledge Fibonacci sequence: 1 1 2 3 5 8 13 21 34 …
Two first numbers: 1
Others: Its value is the sum of 2 previous numbers
Problem Write a C program that will print out the value at the nth
position in
Fibonacci sequence.
Analysis
A position
 int n
Begin
Do {
Accept n;
}
While (n<1);
Print out fibo(n);
End.
Algorithm for
Computing the nth
value of the
Fibonacci sequence
double fibo ( int n) {
int t1=1, t2=1, f=1, i ;
for ( i= 3, i<=n; i++) {
f= t1 + t2;
t1= t2;
t2=f;
}
return f;
}
How to compute the nth value of the Fibonacci sequence
Position 1 2 3 4 5 6 7 8 9 10
1 1 2 3 5 8 13 21 34 55
T1 T2 F

T1 T2 F
T1 T2 F
T1 T2 F
T1 T2 F
T1 T2 F
T1 T2 F …
Program 6:
Related knowledge
Problem Write a C program that will accept a positive integer then print out
whether it is an element of the Fibonacci sequence or not.
Analysis
An integer  int n
Begin
Do {
Accept n;
}
While (n<1);
If ( isFibonacci(n)==1) Print out “It is a Fibonacci element.”;
Else print out “It is not a Fibonacci element.”
End
Algorithm for
Checking whether
an integer is a
element of the
Fibonacci sequence
or not
int isFibonacci (int n)
{ int t1=1, t2=1, f=1;
if (n==1) return 1; /* n belongs to the Fibonacci sequence*/
while (f<n) /* Find out the Fibo number f to n */
{ f= t1 + t2;
t1=t2;
t2=f;
}
return n==f; /* if n==f  n is Fibo element  return 1 */
}
Program 7:
Related knowledge Getting the rightmost digit of the integer n: n%10
Problem Write a C program that will carry out some times. In each time, a
nonnegative integer is accepted then print out the sum of its decimal
digits. The program will terminate when its value of accepted number
is negative.
Analysis
Sum  int S=0
Accepted integer
 int n
Begin
Do
{ Accept n;
If (n>=0)
{ S = sumDigits(n);
Print out S;
}

}
While (n>=0);
End
Algorithm for
Computing sum of
digits of a
nonnegative integer
int sumDigits (int n)
{ int sum=0; /* initialize sum of digits */
Do
{ int remainder = n%10 ; /* Get a digit at unit position */
n = n/10;
sum += remainder;
}
while (n>0);
return sum;
}
Program 8:
Related knowledge Making a real number from its integral part and its fraction (its
fraction must be positive).
Example : 32 25  32.25
25  0.25  32+0.25= 32.25
Example -51 139  -51.139
139  0.139  -51- 0.139= -51.139
double makeDouble(int ipart, int fraction)
{ double d_f= fraction;
while (d_f >=1) d_f = d_f/10; /* create the fraction <1 */
if (ipart<0) return ipart – d_f; /* case -51 – 0.139 */
return ipart + d_f ; /* case 32 + 0.25 */
}
Problem Write a C program that will accept the integral part and fraction of a
real number then print out the this real number.
Analysis
Integral part
 int ipart
Fraction
 int fraction
Real number
 double value
Begin
Accept ipart;
Do
{ Accept fraction;
}
While fraction<0;
value= makeDouble(ipart,fraction);
Print out value;
End
Program 9:
Related knowledge Find out the greatest common divisor (gcd) and least common
multiple (lcm) of two positive integers:
Find out gcd of a and b
a b a b
14 21 13 8

14 7 5 8
7 7 5 3
2 3
2 1
1 1
int gcd( int a, int b)
{ while ( a != b )
if a>b then a -=b;
else b -= a;
return a;
}
int lcm ( int a, int b)
{ return a*b/ gcd(a,b);
}
Problem Write a C program that will accept two positive integers then print out
their greatest common divisor and least common multiple.
Analysis
Two integers
 int a, b
gcd  int d
lcm  int m
Begin
Do
{ Accept a, b;
}
While ( a<=0 OR b <=0);
d = gcd(a,b);
m = lcm (a.b);
Print out d;
Print out m;
End
Program 10:
Related
knowledge
Print out the minimum and the maximum digits of a nonnegative integer
integer
Example: n= 10293  Print out 9, 0
void printMinMaxDigits( int n)
{ int digit; /* Variable for extracting 1 digit */
int min, max ; /* Result variables */
digit = n% 10; /* get the first rightmost digit: 3 */
n=n/10; /* 1029, the remainder needs to proceed after*/
min=max=remainder; /* initialize results */
while (n>0)
{ digit = n%10; /* Get the next digit */
n=n/10;
if (min > remainder) min=remainder; /* update results */
if (max < remainder) max=remainder;
}
Print out min, max;
}

Problem Write a C program that will accept a non-negative integer then print out its
minimum and maximum digits.
Analysis
Noun:
A integer
 int n
Begin
Do
{ Accept n;
printMinMaxDigits(n);
}
While (n<0);
End

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