Before we start
writing a program using loop please consider below:
Understand
the problem domain
identify
the steps which, when taken, will satisfy the program's requirements
Identify
the data needed to solve the problem, and whether the data is being generated
by the program or provided as input
Basically
problem solving with computer need 3 major steps:
Input
Process
Output
Use Analysis tools effectively when
solving the problem.
Basically there are 3 types of loops
1.
While /
While-End loop
2.
Repeat /
Until Loop
3.
Automatic
Counter Loop
What is loop
Loop is a repeatitive structure. It will
repeat a set of instruction several time for different set if date processing.
Most business problems involve in doing
the same task over and over for e.g.
PAYROLL
for employee where the same process on a different set of data.
While / While-End
Algorithm for While/ while-end loop
While
(Condition)
Instruction
Instruction
:
:
While end
The
Flowchart for While-while-end loop
Syntax
in C language for While / while-end loop
while
(condition) {
instruction;
instruction;
:
:
}
Repeat / Until Loop
Algorithm
for Repeat / Until loop
Repeat
Instruction
Instruction
:
:
Until
(condition)
Flowchart
for repeat / until loop
Syntax
in C language for Repeat / until
In
C the repeat / until loop using the do while keyword. In do while loop the
condition will be test at the end of the loop. Instead of false condition will
entering the loop, in do while true will make the control will enter the loop
until the condition is false then the control will exit the loop.
do
{
instruction
instruction
:
:
} while (condition);
Differences
between while / while end and repeat / until loop
1.
While
loop will continue the loop as long as the condition is true, but in repeat /
until loop it will exit loop when the condition is true.
2.
The
while loop, the condition is at the
beginning, but in repeat until the condition is at the end of the loop.
3.
In
while loop the process might not enter the loop but in repeat / until loop, the
process will at least enter the loop once.
When
does we use the while and repeat / until loop
Ussually we will use the both loop when we do not know the
number of times the instruction should repeat.
Examine
the example below:
//program 1
#include <stdio.h>
int main (void) {
int num, total;
scanf(%d,num);
while (num != 0) {
scanf
(%d,num);
total = total + num;
}
printf (Total = \n , total);
return (0);
}
//Program 2
#include <stdio.h>
int main (void) {
int num, total;
scanf(%d,num);
do {
scanf (%d,num);
total = total + num;
} while (num != 0) ;
printf (Total = \n , total);
return (0);
}
Automatic conter loop
This
type of loop, it increament or decreament a variable each time the loop is
processed.
The
variable is use as a counter, that starts counting at a specific number, and
increament or decreament the variable each time the loop is processed.
The
set of instruction within the loop repeats until the counter is greater or
lesser than an ending number.
The
algorithm of automatic counter loop
Loop
: counter = begin to end step
Instruction
Instruction
:
:
Loop-end
: counter
Flowchart for automatic counter loop
The
syntax for a for-loop is
for (expression1; expression2; expression3) { statements }
We noted that each of the expressions in
the loop's control statement is completely optional. The semantics of the
forloop are:
1.
evaluate
expression1;
2.
evaluate
expression2 - if it is TRUE, then do steps 3 and 4 - otherwise, continue at
step 5
3.
do all of
the statements within the body of the for loop
4.
evaluate
expression3 and continue at step 2
5.
(get here
when loop has completed) - carry on execution with the statement immediately
past the body of the for loop
When we usually use the automatic counter
loop.
We usually use the loop when we want to execute
and exact numbers of times of loop.
Consider the program below we are to
print number 1 to 10 and add the number.
#include
<stdio.h>
int main
(void) {
int i,
total;
for (i =
1; i < 11; I++) {
printf(%d,i);
total = total + i;
}
printf(%d,total);
}
Some interesting problems
Increament
It
is a task done by adding a constant such as 1 or 2 to a value of a variable.
For
e.g.
c
= c + 1;
or
c = c + 2;
1
and 2 is adding to a variable constantly.
Accumulating
It
is a task to sum a group of numbers. It is similar to increament but the valu
will be the value of the total numbers.
e.g
totalsale = totalsale + monthlysale;
Sentinel
A
sentinel value is a data value that is impossible in the context of the
problem. It could br use to indicate to a program that some special condition has arisen, and this special
condition ussually use or intend to exit a loop. It ussually use in while and
do while loop.
Relational operators
It turns out that virtually all C-language
expressions may be used as a conditional expression. For now, we will limit our
study only to those involving arithmetic operands and relational operators.
The relational operators are:
== equality.
TRUE when both its operands have the same value NOTE: this operator is not the
same as the assignment operator, =
!= inequality
- TRUE when == is FALSE
< TRUE
when the left operand is less than the right operand
<= TRUE if
the left operand is less than or equal to the right operand
> TRUE when
the left operand is greater than the right operand
>= TRUE when
the left operand is greater than or equal to the right operand
The semantics (logic of the statement) of
the condition statement are to evaluate the conditional expression. Just when the
expression is true, the block of statements is executed. Just when the
expression is false, the block of statements following the exit the loop.