Computer Science Department Relational Operators And Decisions

Computer Science Department Relational Operators A Relational Operator compares two values. Values can be any built-in C++ data type. The comparison involves such relationship as equal to, less than and greater than. The result of the comparison is either true or false.

Computer Science Department Relational Operator MeaningOperator Greater than> Less than< Equal To== Not Equal To!= Greater Than or equal to>= Less Than or equal to<=

Computer Science Department Decisions In a program a decision causes a one-time jump to a different part of the program, depending on the values of an expression. Decision can be made in C++ in several ways. –IF Statement. –IF and ELSE Statement. –Switch Statement.

Computer Science Department IF Statement C++ uses keyword if to implement the decision control instruction. if ( this condition is true ) execute this statement; The if keyword if followed by a test expression in parenthesis. If the condition is true than compiler will execute the immediate statement. But if the condition is false than the immediate statement will not execute, and the compiler will skip the immediate statement and execute the next statement.

Computer Science Department IF Statement Example void main ( ) { int x; cout<<“Enter a number”; cin>> x; if ( x > 100 ) cout<<“the number is greater than 100”; getche( ); }

Computer Science Department Multiple Statements in the IF body if ( condition ) { statement 1; statement 2. statement n; }

Computer Science Department If … else statement Sometimes we want to do one thing if the condition is true and other if the condition is false. That’s where the if.. else statement is used. if ( condition ) { statement 1; statement 2; } else { statement 1; statement 2; }

Computer Science Department If..else Example void main ( ) { float b_salary, m_allowance, h_allowance; cout<<“Enter Basic Salary”; cin>>b_salary ; if ( b_salary >= ) { m_allowance = 40.0 / 100 * b_salary; h_allowance = 30.0 / 100 * b_salary; } else { m_allowance = 30.0 / 100 * b_salary; h_allowance = 20.0 / 100 * b_salary; }

Computer Science Department Nested if..else Statements If we write the entire if..else statement within the body of if statement or else statement. This is called nesting of ifs. if ( condition ) { if ( condition ) statement 1; else statement 2; } else { statement 3; }

Computer Science Department The else..if Construction if (condition1) statement 1; else if (condition2 ) statement 2; else if (condition3) statement 3; else if (condition4) statement 4; else statement 5;

Computer Science Department Else..if example void main ( ) { int month; cout<<“ Enter Month in Number= ” cin>>month; if ( month == 1 ) cout<<“ January”; else if ( month == 2 ) cout << “ February ”; else if ( month == 3 ) cout<< “ March ”;. else cout << “ December ”; }

Computer Science Department LOGICAL OPERATORS

Computer Science Department Logical Operators These operator allows you to logically combines variables or expressions. There are three logical operators – && (for AND Operation) – || ( for OR Operation) – ! ( for NOT Operation)

Computer Science Department Logical AND Operator The AND operator ( && ) requires both relationships to be true in order for the overall result to be true. If either or both of the relationships are false, the entire result is false. Example cout<<“Enter Marks”; cin>> marks; if ( ( marks > 100 ) && ( marks < 0 ) ) cout<< “ Marks are invalid”;

Computer Science Department Logical OR Operator The OR Operator ( || ) takes two logical expressions and combines them. If either or both are true, the result is true. Both values must be false for the result to be false. Example char t_grade, p_grade; cout << “Enter the Theory Grade: P for pass, F for Fail”; cin>> t_grade; cout<< “Enter the Practical Grade: P for pass, F for Fail”; cin>> p_grade; if ( ( t_grade == ‘F’ ) || ( p_grade == ‘F’ ) ) cout<<“Overall Fail”; else cout<<“Overall Pass”;

Computer Science Department Logical NOT Operator The ( && ) and ( II ) operators always appears between two expressions. Also known as binary operators. The NOT operator ( ! ) is a unary operator. It precedes a single logical expression and gives its opposite as a result. Example if !( marks > 50) is same as if (marks <= 50)

Computer Science Department SWITCH STATEMENT

Computer Science Department Switch Statement If you have a large decision tree, and all the decisions depend on the value of the same variable, switch statement is suitable instead of if..else or else..if statement. switch ( integer expression ) { case constant 1: statement 1; case constant 2: statement 2; case constant 3: statement 3; default: statement 4; }

Computer Science Department Switch Statement The integer expression following the keyword switch is an expression that will yield an integer value. It could be an integer constant like 1, 2,or 3, or an expression that evaluates to an integer. The keyword case is followed by an integer or a character constant. The constant in each case must be different from other.

Computer Science Department Example void main ( ) { int i = 2; switch (i) { case 1: cout<<“case 1 \n”; case 2: cout<<“case 2 \n”; case 3: cout<<“case 3 \n”; default: cout<<“default \n”; } Output of the program Case 2 Case 3 default

Computer Science Department Break Statement If we want that only particular case should be executed than break statement should be used to get out of the control structure. int i = 2; switch (i) { case 1: cout<<“case 1 \n”; break; case 2: cout<<“case 2 \n”; break; case 3: cout<<“case 3 \n”; break; default: cout<<“default \n”; }

Computer Science Department Tips of using Switch Statement a)As in the previous examples the cases are arranged in ascending order 1,2,3 and default. You can in fact put the cases in any order you want. b)You are also allowed to use char values in case and switch. c)You can write a case in switch, which is not followed by any statement. As shown in the next example

Computer Science Department Tips of using Switch Statement char ch; cout<<“enter any of the alphabet a, b, or c”; cin>>ch switch(ch) { case ‘a’: case ‘A’: cout<<“you entered a”; break; case ‘b’: case ‘B’: cout<<“you entered b”; break; case ‘c’: case ‘C’: cout<<“you entered c”; }

Computer Science Department Tips of using Switch Statement d)Even if there are multiple statements to be executed in each case there is no need to enclose these within a pair of braces. e)If we have no default case, then the program simply falls through the entire switch and continues with the next instruction that follows the control structure. f)The disadvantage of switch is that one cannot have a case in a switch which looks like case i<=20; All that we can have after the case is an int constant or a char constant. Even a float is not allowed.

Computer Science Department Tips of using Switch Statement g)The break statement when used in a switch takes the control outside the switch. h)In principle, a switch may occur within another, but in practice it is rarely done. i)The switch statement is very useful while writing menu driven programs.

Computer Science Department The Conditional Operator

Computer Science Department Conditional Operator The conditional operator ? and : are sometime called as ternary operators since they take three arguments expression1 ? expression2 : expression3 The above statement means that “ if expression1 is true (i.e. if its value is non-zero), then the value returned will be expression2 otherwise the value returned will be expression3”

Computer Science Department Example int x, y; cin>>x; y = (x>5 ? 3 : 4); cout<< y;

Computer Science Department Points to be noted about Conditional Operators It is not necessary that the conditional operators should be used only in arithmetic statements int i; cin>> i; (i==1 ? cout<<“ hello” : cout<<“helloworld”);

Computer Science Department Points to be noted about Conditional Operators The conditional operators can be nested as shown below int k, num = 30; k=(num>5 ? (num <=10 ? 100 : 200) : 500); cout<< k; The limitation of the conditional operator is that after the ? Or after the : only one C++ statement can occur.