© Janice Regan, CMPT 102, Sept CMPT 102 Introduction to Scientific Computer Programming Logical and Relational Expressions Nested if statements Case statements

© Janice Regan, CMPT 102, Sept Multiple Selections (if-else if-else) if (condition) {/* Series of actions to be taken when the condition is TRUE */ action 1; action n; } else if (condition 2) { /* actions to be taken when condition is FALSE and condition2 is TRUE */ action 1; action n; } else { /*Series of actions to be taken when condition and condition 2 are FALSE */ action 1; action n; }

© Janice Regan, CMPT 102, Sept Defining the condition  Each decision statement is based upon a condition  The condition is an expression with a logical value (true or false)  The condition may be  A relational expression (a type of logical expression) Two numerical values combined using a binary relational operator (a simple relational expression) A more complex relational expression  Another type of logical expression Two logical values combined with a binary logical operator One logical value One logical value operated on by a unary logical operator A more complex logical expression

© Janice Regan, CMPT 102, Sept Precedence of operators in C  ( ) []. innermost first  (pre) + - ! ~(unary) (right to left)  * / %  + -  >=  == !=  &&  ||  = += -= *= /= %=(right to left)

© Janice Regan, CMPT 102, Sept Expressions with relational operators  Value of a relational expression (expression including a relational or binary equality operator) is true or false.  Arguments of a relational operator are numerical (or character)  A < C  (A + B) >= CLet A=9, B=5, C=2  A * B <= C  A % C == A % B  A != -C

© Janice Regan, CMPT 102, Sept Expressions: relational operators  A < C  Let A=9, B=5, C=2 A C < 9 2 F A C < Value of expression is Boolean: In C Boolean (T or F) is represented by an integer. T=0, F any non zero integer

© Janice Regan, CMPT 102, Sept Expressions: relational operators  (A + B) >= C X >= C  Let A=9, B=5, C=2 + A B X C >= T A B C + >= Value of expression is Boolean:

© Janice Regan, CMPT 102, Sept Expressions: relational operators  A * B <= C X <= C  Let A=9, B=5, C=2 * A B X C <= F A B C * <= Value of expression is Boolean:

© Janice Regan, CMPT 102, Sept Expressions: relational operators  Let A=9, B=5, C=2  A % C == A % B X == A % B X == Y % A C X Y A 9 5 % B == F A C % % B 4 Value of expression

© Janice Regan, CMPT 102, Sept Expressions: relational operators  A != -C A != X  Let A=9, B=5, C=2 != A X C T A C - != Value of expression

© Janice Regan, CMPT 102, Sept Importance of order of operations  Order of operations is determined by operator precedence rules () before /  (A + B) / C X / C  Let A=10, B=5, C=2 2 A B C + / + A B X C Value of expression

© Janice Regan, CMPT 102, Sept Expressions: logical operators  Value of a logical expression (expression including a logical operator) is true or false.  Arguments of the logical operator are also true or false Let A=9, B=5, C=2 Then  (C = C  (A C  !(A C  A < B && B < C++

© Janice Regan, CMPT 102, Sept Expressions: logical operators  Let A=9, B=5, C=2  (C = C) X && (A >= C) X && Y < C B X 2 5 T Y A 9 2 >= C && T A C < >= B && T Value of expression

© Janice Regan, CMPT 102, Sept Expressions: logical operators  Let A=9, B=5, C=2  (A C) X || (A > C) X || Y < A B X 9 5 F || T A C < > B Value of expression Y A 9 2 > C T T

© Janice Regan, CMPT 102, Sept Expressions: logical operators  Let A=9, B=5, C=2  !(A C) !X || (A > C) Y || (A > C) Short Circuit < A B X 9 5 F Y T || F A B < ! C Value of expression !

© Janice Regan, CMPT 102, Sept Expressions: logical operators  Let A=9, B=5, C=2  A < B && B < C++ X && B < C++ Short Circuit (increment not evaluated!) < A B X 9 5 F && F A B < C Value of expression

© Janice Regan, CMPT 102, Sept Flowchart for multiple selection condition2 Statement 1; Statement n; T F Statement 1; Statement n; condition F Statement 1; Statement n; T

© Janice Regan, CMPT 102, Sept Multiple Selections (if-else if-else) if (condition) {/* Series of actions to be taken when the condition is TRUE */ action 1; action n; } else if (condition 2) { /* actions to be taken when condition is FALSE and condition2 is TRUE */ action 1; action n; } else { /*Series of actions to be taken when condition and condition 2 are FALSE */ action 1; action n; } NEXT STATEMENT

© Janice Regan, CMPT 102, Sept Multiple Selections (Nested if) if (condition) { /* Series of actions to be taken when the condition is TRUE */ action 1; action n; } else { if (condition 2) { /* Series of actions to be taken when condition is FALSE and condition2 TRUE */ action 1; action n; } else { /* Series of actions to be taken when condition and condition 2 are FALSE */ action 1; action n; }

© Janice Regan, CMPT 102, Sept Flowchart for multiple selection condition2 Statement 1; Statement n; T F Statement 1; Statement n; condition F Statement 1; Statement n; T

© Janice Regan, CMPT 102, Sept Flowchart for multiple selection Statement 1; Statement n; T F condition

© Janice Regan, CMPT 102, Sept Multiple Selections (Nested if) if (condition) { if (condition 2) { /* Series of actions to be taken when condition is FALSE and condition2 TRUE */ action 1; action n; } else { /* Series of actions to be taken when condition and condition 2 are FALSE */ action 1; action n; } else { /* Series of actions to be taken when the condition is TRUE */ action 1; action n; }

© Janice Regan, CMPT 102, Sept Flowchart for multiple selection condition2 Statement 1; Statement n; F T Statement 1; Statement n; condition F Statement 1; Statement n; T

© Janice Regan, CMPT 102, Sept Flowchart for multiple selection Statement 1; Statement n; F T condition

© Janice Regan, CMPT 102, Sept The switch statement  An alternative method to if statements with multiple else clauses  The controlling expression (selector) must have an integral type  Characters also work because they can be converted to integers  Case labels are particular values of the controlling expression  Break statements exit from the switch structure

© Janice Regan, CMPT 102, Sept switch Structures switch(controling expression) { case value1: statements1; break; case value2: statements2; break;... case valuen: statementsn; break; default: statements; }

© Janice Regan, CMPT 102, Sept switch Statement expression = value1 expression = value2 expression = valuen

© Janice Regan, CMPT 102, Sept Sample case statement /* This is in a loop that reads */ /* nextChar each time */ while ( endInput != nextChar ) { switch (nextChar) { case 0: count1++; break; case 1: count2++; break; case 2: count3++; break; case 4: count4++; break; case 5: count5++; break; case 6: count6++; break; case 7: count7++; break; default: countOther++; }