Lecture 10 - Control Structures 2

Control Structures (Part 2)
Md. Imran Hossain Showrov (showrovsworld@gmail.com)
10
1

Outline
 The do-while Statement
 The for Statement
 Difference between for, while & do-while
 The switch Statement
 The break Statement
 The continue Statement

The do-while Statement
 When a loop is constructed using the while statement ,
the test for continuation of the loop is carried out at the
beginning of each pass.
 Sometimes, it is desirable to have a loop with the test for
continuation at the end of each pass.
 The general form of the do-while statement is
do statement while (expression) ;
Here, the statement will be executed repeatedly, as long as the
value of expression is true.

The do-while Statement: the Key Point
 For do – while statement, we have to remember that
the statement will always be executed at least once,
since the test for repetition does not occur until the
end of the first pass through the loop.
 For many applications it is more natural to test for
continuation of a loop at the beginning rather than at
the end of the loop. For this reason, the do-while
statement is used less frequently than the while
statement.

The do-while Statement: Example 1
// Program to display the consecutive digits 0,1,2,…,9
main()
{
int digit = 0;
do {
printf(“%dn”, digit++);
} while (digit <= 9 );
}

The do-while Statement: Example 2
// Program to find the average of a list of numbers
main()
{
int n, count = 1;
float x, average, sum = 0;
printf(“How many numbers: ”);
scanf(“%d”, &n);
do {
printf(“x = ”);
scanf(“%f”, &x);
sum +=x;
++count;
} while (count <= n );
average = sum / n;
printf(“nThe average is: %fn”, average);
}

The for Statement
 The for statement is the most commonly used looping
statement in C.
 This statement includes an expression that specifies an initial
value for an index, another expression that determines
whether or not the loop is continued, and a third expression
that allows the index to be modified at the end of each pass.
for (expression 1; expression 2; expression 3)
statement
Where, expression 1 is used to initialize some parameter that controls the
looping action, expression 2 represents a condition that

The for Statement (cont..)
 The general form of for statement is:
statement
Where, expression 1 is used to initialize some parameter that
controls the looping action, expression 2 represents a condition
that must be true for the loop to continue execution, and
expression 3 is used to alter the value of the parameter initially
assigned by expression 1.

The for Statement to the while statement
In for Statement
statement
Conversion into while statement
expression 1;
while(expression 2)
statement
expression 3 ;

The for Statement (Example)
 Example: Suppose we want to display the consecutive
digits 0,1,2,…..,9, with one digit on each line.This can
be accomplished with the following program.
Solution:
●
main()
●
{
●
int digit;
●
for(digit = 0; digit<=9; ++digit)
●
printf(“%dn”,digit);
●
}

The for Statement (More Examples)
// Program to calculate the sum of first n natural numbers
// Positive integers 1,2,3...n are known as natural numbers
main()
{
int num, count, sum = 0;
printf("Enter a positive integer: ");
scanf("%d", &num);
for (count = 1;count <= num; count++) {
sum += count;
}
printf("Sum = %d", sum);
}

The for Statement (More Examples)
// Program to calculate the average of first n natural numbers
// Positive integers 1,2,3...n are known as natural numbers
main()
{
int num, count, sum = 0;
float average;
printf("Enter a positive integer: ");
scanf("%d", &num);
for (count = 1;count <= num; count++)
sum += count;
average = sum/num;
printf(“Average = %f", average);
}

Difference b/n for, while & do-while
No For loop While loop Do while loop
1.
Syntax: for(initialization;
condition;updating),
{ Statements; }
Syntax:
while(condition), { .
Statements; . }
Syntax: do { Statements;
} while(condition);
2.
It is known as entry
controlled loop
It is known as entry
controlled loop.
It is known as exit
controlled loop.
3.
If the condition is not
true first time than
control will never enter in
a loop
If the condition is not
true first time than
control will never
enter in a loop.
Even if the condition is
not true for the first time
the control will enter in a
loop.
4.
There is no semicolon;
after the condition in the
syntax of the for loop.
There is no
semicolon; after the
condition in the
syntax of the while
loop.
There is semicolon; after
the condition in the
syntax of the do while
loop.
5.
Initialization and
updating is the part of
the syntax.
Initialization and
updating is not the
part of the syntax.
Initialization and
updating is not the part
of the syntax

The switch Statement
 The switch statement causes a particular group of
statements to be chosen from several available groups.
 The selection is based upon the current value of an
expression which is included within the switch statement.
 The general form of switch statement is
switch (expression) statement
 Where, expression results in an integer value. Note that
expression may also be of type char, since individual
characters have equivalent integer values.

The switch Statement (Example 1)
//A simple switch program where choice is char type
switch(choice = getchar()) {
case ‘r’:
case ‘R’:
printf(“Red”);
break;
case ‘w’:
case ‘W’:
printf(“White”);
break;
case ‘b’:
case ‘B’:
printf(“Black”);
}

The switch Statement (Example 3)
//A simple switch program where flag is int. x and y are floating-point.
switch(flag) {
case -1:
y = abs(x);
break;
case 0:
case 1:
y = sqrt(x);
break;
default:
y = 0;
}

The break Statement
 The break statement is used to terminate loops or
to exit from a switch.
 It can only be used within a for, while, do-while or
switch statement.
 The break statement is written simply as
break;
 Without any embedded expression or statement.

The break Statement (example)
//scan positive natural number between 1 to 100
scanf(“%f”, &x);
while(x <= 100){
if(x < 0){
printf(“Error- negative number”);
break;
}
scanf(“%f”,&x);
}

The continue Statement
 The continue statement is used to bypass the remainder of
the current pass through a loop.
 The loop does not terminate when a continue statement is
encountered.
 Rather, the remaining loop statements are skipped and
the computation proceeds directly to the next pass
through the loop.
 The continue statement can be included within a while, do-
while and a for statement
continue;

The continue Statement
//print 0 to 8 except 4.
for (int j=0; j<=8; j++)
{
if (j==4)
{
continue;
}
printf("%d ", j);
}

Lecture 10 - Control Structures 2

Lecture 10 - Control Structures 2

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Lecture 10 - Control Structures 2