Chapter 3 Computer Programmingodp-1_250331_041044.pdf

Computer Programming
[ECEg-1052]
Chapter Three:
Control Statements
Prepared by Electronics and Computer Engineering Stream.

Outline
 Introduction
 Conditional Structure: If and else
 Repetitive Structures or loops
 Bifurcation of control and jumps.
 The selective Structure: switch

4.1. Introduction

Control statements allow decision making within programs.

Control statements come in several different forms:
➔
Conditional statements: to optionally execute C++ statements
➔
Loops: execute statements repeatedly until the exit condition is
satisfied.
➔
Branch: jump to a certain statement and continue execution.
3

4.2. Conditional Structure: if and else
 It is used to execute an instruction or block of instructions only if a
condition is fulfilled.
 if can be used in different forms depending upon nature of conditional test.
1. if
2. if…else
3. Nested – if
4

Simple if statement
General form:
5
if (test expression)
{
statement-block;
}
statement-x;
Test expression
?
Statement-x
Statement-block
True
False
Entry
Flowchart of simple if statement
General form

Cont’d...
 The ‘statement-block’ may be a single statement or a group of statements.
 If the test expression is true, the statement-block is executed.
 If it is false, statement-block is ignored (not executed) and the program
continues on the next instruction after the conditional structure.
6

Cont’d...
* To display number is positive.*/
#include <iostream>
using namespace std;
int main(){
int num;
cout<<"Enter a number:";
cin>>num;
if (num>0)
cout<<" number is positive ";
return 0;
} 7
Sample output 1:
Enter a number: 3
number is positive
Sample Output 2:
Enter a number:-3

Cont’d...

For a block of instructions, we use curly brackets { }:
Example:
if (x == 100){
cout << "x is ";
cout << x;
}

But for a single, we can ignore {}.
Example:
if (x == 100)
cout << "x is 100";
8

The if – else statement
Form:
9
if (condition)
{
statement block 1;
}
else
{
statement block 2;
}
statement-x;
Condition
?
statement block
1
statement-x
statement block
2
Entry
False
True

Cont’d...
For example:
if (x == 100)
cout << "x is 100";
else
cout << "x is not 100";
10

Nested if statement

When a series of decisions are involved, use more than one if…else
statement.
Example:
11
Exercise
Write a program that find whether the given number is even or odd.
if (x>0)
cout<<"The given number is +ve"<<endl;
else if (x<0)
cout<<"The given number is negative"<<endl;
else
cout<<"The given number is zero";

Solution
// To find whether given number is even or odd.
#include<iostream>
int main(){
int no;
cout<<"enter a number";
cin>>no;
if ( no %2 == 0 )
cout<<no<<"is an even number";
else
cout<<no<<"is an odd number";
}
12
Cont’d...

4.2 Repetitive Structures or loops
 Loops have as objective to repeat a statement a certain number of
times while a condition is fulfilled.

The while loop

The do-while loop

The for loop
13

The while loop
Format:
while(expression)
statements;
14
While
(expression)
?
statements
False
True
Out of loop

Cont’d...
Example:
/* Find the sum of even
numbers between 1 to n */
#include <iostream>
int main(){
int i, n, sum=0;
cout<<"enter the end number:";
cin>>n;
15
i=2;
while (i <= n){
sum = sum + i;
i = i + 2;
}
cout<<"sum= "<<sum;
}

The do-while loop
Format:
do
statements;
while (condition);
16
Condition
?
statements
False
True
Out of loop
do

Example
sum = 0;
i = 1;
do{
sum += i;
i += 2;
} while (i <= 100);
cout<<“Sum of odd integers up to 100 is”<<sum;
Output:
Sum of odd integers up to 100 is 2500
17
Cont’d...

The for loop
 Its format is:
for (initialization; condition; increase/decrease)
statement;
 Following steps are involved in the code:
Initialization condition checking body of the loop increment/ decrement
again condition checking
18

19
initialization
increase/decrease
statement
Condition
?
Out of loop
False
True
Cont’d...

Example 1:
sum = 0;
for (i=0 ; i <= 100 ; i++)
sum += i;
Example 2: Write a program to list a number and its square in two columns
for integers 1 up to 10.
20
Cont’d...

#include<iostream>
int main(){
for(int i=1;i<=10;i++) {
cout<<"The number is:"<<i;
int square=i*i;
cout<<" and its square is:"<<square;
cout<<endl;
}
} 21
Cont’d...

4.3 Bifurcation of control and jumps.
The break instruction
 The format of the break statement is simply
break;
 Causes an immediate exit even if the condition for its end is not fulfilled.
 It can be used to end an infinite loop, or to force it to end before its
natural end.
22

Examples
i=1;
while (1){
cout<<i<<" ";
if (i==10)
break;
i=i+1;
}
Output: 1 2 3 4 5 6 7 8 9 10
23
Cont’d...

Output
10, 9, 8, 7, 6, 5, 4, 3, countdown
aborted!
24
Cont’d...
// break loop example
#include <iostream>
int main (){
int n;
for (n=10; n>0; n--) {
cout << n << ", ";
if (n==3){
cout << "countdown aborted!";
break;
}
}
return 0;
}

The continue instruction
Format: continue;
 The continue statement tells the compiler, “Skip the following statements
and continue with the next iteration’’.
 In while and do loops, continue causes the control to go directly to the
test-condition and then to continue the iteration process.
 In the case of for loop, the increment section of the loop is executed before
the test-condition is evaluated.
25

while (---------)
{
---------
---------
if (condition)
continue;
---------
---------
}
--------
26
Cont’d...

// to add only positive numbers
#include<iostream>
int main(){
int i, n, sum=0;
cout<<"enter any 10 numbersn";
for(i=1;i<=10;i++) {
cin>>n;
if (n==7)
continue;
sum += n;
}
cout << " sum of +ve numbers = "<<sum;
}
27
Cont’d...

// example
#include <iostream>
int main (){
for (int n=10; n>0; n--) {
if (n==5)
continue;
cout << n << ", ";
}
cout << "End!";
return 0;
} 28
Cont’d...
Output:
10, 9, 8, 7, 6, 4, 3, 2, 1, End!

The goto instruction
 Allows making an absolute jump to another point in the program.
 The destination point is identified by a label, which is then used as an
argument for the goto instruction.
 A label is made of a valid identifier followed by a colon (:).
29

// goto loop example
#include <iostream>
int main (){
int n=10;
loop:
cout << n << ", ";
n--;
if (n>0)
goto loop;
cout << "End!";
return 0;
}
30
Cont’d...
Output:
10, 9, 8, 7, 6, 5, 4, 3, 2, 1, End!

The exit function
 A function defined in cstdlib(stdlib.h) library.
 The purpose of exit is to terminate the running program with an specific
exit code.
 Its prototype is:
void exit (int exit code);
 if exit code= 0 means that the program finished normally.
31

// exit function example
#include <iostream>
#include <cstdlib>
int main (){
int n=10;
while(n>0) {
cout << n << ", ";
n--;
if (n==6)
exit(0);
}
cout <<"End!";
return 0;
} 32
Cont’d...
Output:
10, 9, 8, 7,

The selective Structure: switch
General form:
33
switch (expression)
{
case constant1:
block of instructions 1;
break;
case constant2:
block of instructions 2;
break;
…
default:
default block of instructions;
}
 Inclusion of break at the end of each
block is necessary because if, for
example, we did not include it after
block of instructions 1 the program
would not jump to the end of the
switch selective block (}) and
continue to execute the rest of the
blocks of instructions until the first
appearance of break.

Example 1:
switch (x) {
case 1:
cout << "x is 1";
break;
case 2:
cout << "x is 2";
break;
default:
cout << "value of x unknown";
} 34
Cont’d...
Example 2:
switch (x) {
case 1:
case 2:
case 3:
cout << "x is 1, 2 or 3";
break;
default:
cout << "x is not 1, 2 nor 3";
}

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