Logical Operators and Precedence Mr Crone Logical Operators

Logical Operators and Precedence Mr. Crone

Logical Operators • C++ includes three logical operators that allow us to create complex conditions Three Logical Operators: • && • || • !

And - && • The “&&” symbol represents And • The “&&” symbol can be placed between two relational expressions – both expressions must be true in order for the entire condition to be evaluated to true Example) int x=4, y = 7; if((x<y) && (y >0)) cout << “Both conditions are true. ”;

And - && Example) int x=10, y = 7; if((x<y) && (y >0)) cout << “Option 1”; else cout << “Option 2”;

And - && Example) int x=10, y = 7; if((x<y) && (y >0)) // x < y is not true – condition is false cout << “Option 1”; else cout << “Option 2”; // Option 2 is printed

Or - || • The “||” symbol represents Or • The “||” symbol can be placed between two relational expressions – only one expression must be true in order for the entire condition to be evaluated to true Example) int x=4, y = 4; if((x<y) || (y >0)) cout << “At least one condition is true. ”;

Or - || Example) int x=10, y = 7; if((x<y) || (y >0)) cout << “Option 1”; else cout << “Option 2”;

Or - || Example) int x=10, y = 7; if((x<y) || (y >0)) // y > 0 is true, entire condition is true cout << “Option 1”; // Option 1 is printed else cout << “Option 2”;

Not - ! • The “!” symbol represents Not • The “!” symbol can be placed in front of any relational expression • The “Not” operator changes an expression to its opposite state Example) int x = 5; if(!(x>0)) cout << “Option 1”; else cout << “Option 2”;

Not - ! • The “!” symbol represents Not • The “!” symbol can be placed in front of any relational expression • The “Not” operator changes an expression to its opposite state Example) int x = 5; if(!(x>0)) // condition evaluates to false cout << “Option 1”; else cout << “Option 2”; // prints Option 2

Not - ! Example) int x=10, y = 7; if(!(y >x)) cout << “Option 1”; else cout << “Option 2”;

Not - ! Example) int x=10, y = 7; if(!(y >x)) // Evaluates to true cout << “Option 1”; // Prints Option 1 else cout << “Option 2”;

Precedence of Operators • Logical operators in C++ can have difference precedence just as mathematical operators do Example) 4+3*5 In the statement above, multiplication has a higher precedence than addition

Precedence of Operators Operator Order of Precedence 1. !, unary -, ++, -2. *, /, % 3. +, 4. <, <=, >, >= 5. ==, != 6. && 7. || 8. =, +=, -=, *=, /=

Precedence of Operators • AND has higher precedence than OR Example) (x<y) && (x>0) || (y>0) is the same as saying ((x<y) && (x>0)) || (y>0)

Precedence of Operators • Modulus has the same precedence as multiplication and division • Statements that combine these three operators should be evaluated left to right Example) 4*5%3/2 20 % 3 / 2 2/ 2 1