1. CSC113: Computer Programming (Theory = 03, Lab = 01)
Momina Moetesum
Computer Science Department
Bahria University, Islamabad

2. Control structures – I if / if-else statements
Week # 3

3. Decision Making: Equality and Relational Operators
Lower precedence than arithmetic operators

4. 2 // Using if statements, relational
1 // Fig. 1.14: fig01_14.cpp
2 // Using if statements, relational
3 // operators, and equality operators
4 #include <iostream> 5
6 using std::cout; // program uses cout
7 using std::cin; // program uses cin
8 using std::endl; // program uses endl 9
10 int main()
11 {
12 int num1, num2; 13
14 cout << "Enter two integers, and I will tell you\n"
<< "the relationships they satisfy: ";
16 cin >> num1 >> num2; // read two integers 17
18 if ( num1 == num2 )
cout << num1 << " is equal to " << num2 << endl; 20
21 if ( num1 != num2 )
cout << num1 << " is not equal to " << num2 << endl; 23
24 if ( num1 < num2 )
cout << num1 << " is less than " << num2 << endl; 26
27 if ( num1 > num2 )
cout << num1 << " is greater than " << num2 << endl; 29
30 if ( num1 <= num2 )
cout << num1 << " is less than or equal to "
<< num2 << endl; 33
1. Load <iostream>
2. main
2.1 Initialize num1 and num2
2.1.1 Input data
2.2 if statements
Notice the using statements.
Enter two integers, and I will tell you
the relationships they satisfy: 3 7
The if statements test the truth of the condition. If it is true, body of if statement is executed. If not, body is skipped.
To include multiple statements in a body, delineate them with braces {}.
3 is not equal to 7
3 is less than 7
3 is less than or equal to 7

5. 2.3 exit (return 0) Program Output
34 if ( num1 >= num2 )
cout << num1 << " is greater than or equal to "
<< num2 << endl; 37
38 return 0; // indicate that program ended successfully
39 }
2.3 exit (return 0)
Program Output
Enter two integers, and I will tell you
the relationships they satisfy: 3 7
3 is not equal to 7
3 is less than 7
3 is less than or equal to 7
Enter two integers, and I will tell you
the relationships they satisfy: 22 12
22 is not equal to 12
22 is greater than 12
22 is greater than or equal to 12
Enter two integers, and I will tell you
the relationships they satisfy: 7 7
7 is equal to 7
7 is less than or equal to 7
7 is greater than or equal to 7

6. Precedence and associativity of operrators
Operators
Associativity
Type
( )
Left to Right
Parentheses
* / %
Multiplicative
Additive
<< >>
Stream insertion / extraction
< <= > >=
Relational
== !=
Equality =
Right to Left
Assignment

7. Common programming errors
Syntax error will occur if there is a space between ==,<=,>= or !=
Another syntax error is to reverse their order
Confusing equality operator (==) with assignment operator (=) causes logical error

8. Program control
Specifies the order in which statements are to executed
Sequential execution
Statements executed one after the other in the order written
Transfer of control
When the next statement executed is not the next one in sequence

9. Structured-Programming
Programs are easier to understand, test, debug and, modify.
Rules for structured programming
Only single-entry/single-exit control structures are used
(Bohm and Jacopini) Rules:
1) Begin with the “simplest flowchart”.
2) Any rectangle (action) can be replaced by two rectangles (actions) in sequence.
3) Any rectangle (action) can be replaced by any control structure (sequence, if, if/else, switch, while, do/while or for).
4) Rules 2 and 3 can be applied in any order and multiple times.

10. Control Structures
All programs can be broken down into 3 control structures
Sequence structure
Built into C++. Programs executed sequentially by default.
Selection structures
C++ has three types - if, if/else, and switch
Any selection can be rewritten as an if statement
Repetition structures
C++ has three types - while, do/while, and for
Any repetition structure can be rewritten as a while statement

11. Flowchart Flowchart single-entry/single-exit control structures
Graphical representation of an algorithm
Drawn using certain special-purpose symbols connected by arrows called flowlines.
Rectangle symbol (action symbol)
Indicates any type of action.
Oval symbol
indicates beginning or end of a program, or a section of code (circles).
single-entry/single-exit control structures
Connect exit point of one control structure to entry point of the next (control-structure stacking).
Makes programs easy to build.

12. Structured-Programming
Representation of Rule 3 (replacing any rectangle with a control structure)
Rule 3

13. The if Selection Structure
Single selection structure
used to choose among alternative courses of action
Pseudocode example:
If student’s grade is greater than or equal to 60
Print “Passed”
If the condition is true
print statement executed and program goes on to next statement
If the condition is false
print statement is ignored and the program goes onto the next statement
Indenting makes programs easier to read
C++ ignores whitespace characters

14. The if Selection Structure
Translation of pseudocode statement into C++:
if ( grade >= 60 ) cout << "Passed";
Diamond symbol (decision symbol)
indicates decision is to be made
Contains an expression that can be true or false.
Test the condition, follow appropriate path
if structure is a single-entry/single-exit structure

15. The if Selection Structure
Flowchart of pseudocode statement
true
false
grade >= 60
print “Passed”
A decision can be made on any expression.
zero - false
nonzero - true
Example:
3 - 4 is true

16. Self Practice
Test if the value of the variable count is greater than 10. If it is, print “Count is greater than 10”.
Test if the variable number is not equal to 7, print “The variable number is not equal to 7”.

17. The if/else Selection Structure
Double Selection Structure if
Only performs an action if the condition is true
if/else
A different action is performed when condition is true and when condition is false
Pseudocode
if student’s grade is greater than or equal to 60 print “Passed”
else
print “Failed”
C++ code
if ( grade >= 60 ) cout << "Passed"; else cout << "Failed";

18. The if/else Selection Structure
true
false
print “Failed”
print “Passed”
grade >= 60

19. Ternary conditional operator (?:)
Takes three arguments
condition,
value if true,
value if false
Our pseudocode could be written:
cout << ( grade >= 60 ? “Passed” : “Failed” );

20. Self practice Pseudocode Write C++ statement using: If/else statement
if person’s age is less than or equal to 18 print “Child”
else
print “Adult”
Write C++ statement using:
If/else statement
Ternary conditional operator

21. The if/else Selection Structure
Nested if/else structures
Test for multiple cases by placing if/else selection structures inside if/else selection structures.
if student’s grade is greater than or equal to Print “A” else if student’s grade is greater than or equal to Print “B” else if student’s grade is greater than or equal to Print “C” else if student’s grade is greater than or equal to Print “D” else
Print “F”
Once a condition is met, the rest of the statements are skipped

22. The if/else Selection Structure
Compound statement:
Set of statements within a pair of braces
Example:
if ( grade >= 60 ) cout << "Passed.\n"; else { cout << "Failed.\n"; cout << "You must take this course again.\n"; }
Without the braces,
cout << "You must take this course again.\n";
would be automatically executed
Block
Compound statements with declarations

23. Errors Syntax errors Logic errors Errors caught by compiler
Errors which have their effect at execution time
Non-fatal logic errors
program runs, but has incorrect output
Fatal logic errors
program exits prematurely

24. Self Practice -Identify and correct errors
1) if (gender == 1)
cout<<“woman”<<endl;
else;
cout<<“man”<<endl;
2) if (c< 7);
cout<< “c is less than 7 \n”;
3) if (c=> 7)
cout<< “c is equal to or greater than 7 \n”;

25. Self Practice
Write a C++ program that takes two positive integers from the user and then prints the larger number followed by the words “is larger”. If the numbers are equal, prints the message “These numbers are equal”.