8:01 PM
Cisco, CCNA Exam and Answer
Lecture 4
Algorithm
The solution of any computing problem
involves a series of action in a specific order. This procedure of solving
problems is called algorithm. For example, the going to class algorithm of a
student involves-
However, if you slightly change the order
of the procedure as follows-
- Get out of bed
- Brush the teeth
- Finish toilet
- Get dressed
- Get Shower
- Take breakfast
- Go to the class
Then the student must let his/her dress get
wet. Specifying the order in which the program will be executed is called program
control.
Pseudocode
Pseudocode is an
outline of a program,
written in a form that can easily be converted into real programming statements.
Pseudocode cannot be compiled
nor executed, and
there are no real formatting or syntax rules. It is simply one step - an
important one - in producing the final code. The benefit of
pseudocode is that it enables the programmer to
concentrate on the algorithms
without worrying about all the syntactic details of a particular programming
language. In fact, you can write pseudocode without even knowing what
programming language you will use for the final implementation.
The if Selection Structure
A selection
structure is used to choose among alternative courses of action.
if student’s
grade is more than 40
print “passed”
next
pseudocode statement
In this
pseudocode, if grade of a student is more than 40 then the print command
will be executed. Otherwise, if the student’s grade is not more than 40, the
compiler will move to next pseudocode statement. So, as a general form,
we can see the if selection structure as-
if
(condition){
body of if
}
The condition needs to be true to
get into the body of if. Otherwise, the compiler will go to the next
segment of codes.
The pseudocode can be written in C as-
if
(grade>40)
printf (“Passed \n”);
The if/else Selection Structure
The if selection structure performs an
indicated action only when the condition is true. Otherwise, the action is
skipped. The if/else structure allows the programmer to specify that different
actions are to be performed when the condition is true and when the condition
is false.
if student’s
grade is more than 40
print “passed”
else
print “failed”
If the condition
of if is true, then compiler will print passed and if the condition of
if is false, the compiler will print failed. So, as a general form, we
can see the if/else selection structure as-
if
(condition){
body of if
}
else{
body of else
}
The pseudocode can be written in C as-
if
(grade>40)
printf (“Passed \n”);
else
printf (“Failed \n”);
Note- An if structure may not have any else statement followed by it but
an else structure must have an if structure preceded.
The if/else if/else Selection Structure
Now, consider a
big scenario where you may require a nested if else structure.
if student’s
grade is more than 90
print “Grade: A”
else
if student’s grade is more than
80
print “Grade: B”
else
if student’s grade is more than
70
print “Grade: C”
else
if student’s grade is more than
60
print “Grade: D”
else
if student’s grade is more than
50
print “Grade: E”
else
print “Grade: F”
The program to
provide the desired output is shown here.
#include<stdio.h>
#include<conio.h>
void
main(){
int
grade;
printf("Enter
your grade: ");
scanf("%d",&grade);
if
(grade>90)
printf("Grade: A");
else if (grade>80)
printf("Grade: B");
else if (grade>70)
printf("Grade:
C");
else if (grade>60)
printf("Grade: D");
else if (grade>50)
printf("Grade: E");
else
printf("Grade: F");
getch();
}
If you provide
your number 80, the program will tell you that your grade is C. What happens
here can be debugged by pressing F7 continuously until the program reaches the
end.
1.
clrscr ( ); The output screen
is cleared.
2.
int grade; A location in the
memory is created and grade indicates that location, currently holding a
garbage value.
3.
printf (“…”); Prints the string
on the output.
4.
scanf(“…”, …); Scans the number
from the user and puts that value into the memory location where grade
is pointing. The garbage value is destroyed.
5.
if (…) the condition is false.
Hence, compiler won’t go into if body.
6.
else if (…) the condition is
false. Hence, compiler won’t go into the body of the first else if.
7.
else if (…) the condition is
true. Hence, compiler will print Grade: C.
8.
The compiler ignores all other
else if there and the last else. It reaches getch() and waits for a key-stroke.
Now, guess what
happens if we replace the above code as follows-
#include<stdio.h>
#include<conio.h>
void
main(){
int
grade;
printf("Enter
your grade: ");
scanf("%d",&grade);
if (grade>90)
printf("Grade: A");
if (grade>80)
printf("Grade: B");
if (grade>70)
printf("Grade:
C");
if
(grade>60)
printf("Grade:
D");
if
(grade>50)
printf("Grade:
E");
else
printf("Grade: F");
getch();
}
This program
will output Grade: C Grade: D Grade: E- this is not desirable.
Increment and Decrement Operators
C provides the
unary increment operator ++ and unary decrement operator --. If a variable a is
incremented by 1, the increment operator ++ can be used instead of expression
a=a+1. But the meaning differs based on the place of the operator to the
variable.
|
a++ means use the current value of a in the expression then
increase a by 1.
|
|
++a means
increase the current value of a by 1 and then use the value in expression.
|
|
a-- means use
the current value of a in the expression then decrease a by 1.
|
|
--a means
decrease the current value of a by 1 and then use the value in expression.
|
If unary
increment/ decrement operators are placed in front of the variable, they are
called preincrement/ predecrement operators otherwise they are called
postincrement/ postdecrement operators.
#include<stdio.h>
#include<conio.h>
void
main(){
int a=5, b=10;
printf("%d\n", a);
printf("%d\n", a++);
printf("%d\n", a);
a=5;
printf("%d\n", a);
printf("%d\n", ++a);
printf("%d\n", a);
printf("%d\n", b);
printf("%d\n", b--);
printf("%d\n", b);
b=10;
printf("%d\n", b);
printf("%d\n", --b);
printf("%d\n", b);
getch();
}
The
output of the program is-
5
5
6
5
6
6
10
10
9
10
9
9
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