1. Control Structures Selection
Dr. Khizar Hayat
Associate Prof. of Computer Science

2. Control structures
A program usually follows the sequence in which it’s statements are written.
However it may deviate from linear sequence and
may either repeat a given block of code or
take decision to execute or skip certain block.
C++ provides control structures for these two purposes.
A block or a compound statement is a group of statements inside the delimiters ‘{}’, i.e. {
statement 1;
statement 3; . }
As already discussed, there are three control structures
Sequence (programs execute sequentially, by default)
Selection – the if, if else, switch
Repetition – while , do… while, for

3. Algorithm to input two numbers and print the smaller number
//using if-else
#include<iostream>
using namespace std;
int main() {
int num1, num2;
cout<<"Enter the 1st Number"<<endl;
cin>>num1;
cout<<"Enter the 2nd Number"<<endl;
cin>>num2;
if(num1<num2)
{ //the then part
cout<<num1<<“ is minimum"<<endl; }
else //the else part
cout<<num2<<“ is minimum"<<endl;
return(0);
Start
Pseudocode
begin
get num1
get num2
if num1 < num2
then display num1 as smaller
else display num2 as smaller
end if
end
Read Num1
Read Num2
Num1 < Num2? No
Yes
Display
Num1 as min
Display
Num2 as min
Stop

4. Algorithm to input two numbers and print the smaller number
//using the ternary operator (?:)
#include<iostream>
using namespace std;
int main() {
int num1, num2, min;
cout<<"Enter the 1st Number"<<endl;
cin>>num1;
cout<<"Enter the 2nd Number"<<endl;
cin>>num2;
num1<num2?(min=num1):(min=num2);
cout<<min<<“ is minimum"<<endl;
return(0); }
Start
Pseudocode
begin
get num1
get num2
if num1 < num2
then display num1 as smaller
else display num2 as smaller
end if
end
Read Num1
Read Num2
Num1 < Num2? No
Yes
Display
Num1 as min
Display
Num2 as min
Stop

5. Structure of if statement
if (logical condition)//evaluates to true or false //executed only if logical condition is true { //one or more statements here } else //executed only if logical condition is false //optional part

6. Example 2 #include<iostream> using namespace std; int main() {
// for a single statement you can ignore the delimiters ({}) of if and else
#include<iostream>
using namespace std;
int main() {
float number;
cout<<"Enter the Value for Number"<<endl;
cin>>number;
if(number>=0) //never use semicolon (;) here
cout<<"The given number is Positive"<<endl;
else //never use semicolon (;) here
cout<<"The given number is Negative"<<endl;
return(0); }

7. Example 2
// for a single statement you can ignore the delimiters ({}) of if and else
#include<iostream>
using namespace std;
int main() {
float number;
cout<<"Enter the Value for Number"<<endl;
cin>>number;
if(number>=0) //never use semicolon (;) here
cout<<"The given number is Positive"<<endl; }
else //never use semicolon (;) here
cout<<"The given number is Negative"<<endl;
return(0);
/*It is strongly recommended to use the delimiters ({}), even if a single statement
Advantage: READIBILITY*/

8. Example 3
#include<iostream> using namespace std; int main() { int number; cout<<"Enter the Value for Number"<<endl; cin>>number; if(number%2==0) //never use semicolon (;) here cout<<"The given number is EVEN"<<endl; } else //never use semicolon (;) here cout<<"The given number is ODD"<<endl; return(0);

9. Example 4 //The if block is possible without else
#include<iostream>
using namespace std;
int main() {
float maqsoom, maqs_alaih, quotient;
cout<<"Enter the Value of Dividend"<<endl;
cin>>maqsoom;
cout<<"Enter the Value of Divisor"<<endl;
cin>>maqs_alaih;
if(maqs_alaih==0)
//cout<<"The divisor must not be zero"<<endl;
maqs_alaih= ; //just a small number in place of zero }
quotient= maqsoom/maqs_alaih;
cout<<"The result is "<<quotient<<endl;
return(0);

10. Example 5
#include<iostream> using namespace std; int main() { char letter; cout<<"Enter the character"<<endl; cin>>letter; if((letter=='a')||(letter=='A')||(letter=='e')||(letter=='E')||(letter=='i')||(letter=='I')||(letter=='o')||(letter=='O') ||(letter=='u')||(letter=='U')) cout<<"The given character is Vowel"<<endl; } else cout<<"The given character is not vowel"<<endl; return(0);