coen 244 - 4 - control statement

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4Control

Statements


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Control Structures- Only three control structures are needed to implement any program,

• Sequence structure Program statements are executed sequentially by default

• Selection structures if, if…else, switch

• Repetition structures while, do…while, for

– Structures are combined in one of two ways• Control statement stacking

Connect exit point of one to entry point of the next• Control statement nesting


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4.5 if Selection Statement

• Single Selection statement– Pseudocode

• If student’s grade is greater than or equal to 60 print “Passed”

• if ( grade >= 60 )

cout << "Passed";


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4.6 if…else Double-Selection Statement

• 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";


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4.6 if…else Double-Selection Statement (Cont.)

• Ternary conditional operator (?:)– Three arguments (condition, value if true, value if false)

• Code could be written:– cout << ( grade >= 60 ? “Passed” : “Failed” );

Condition Value if true Value if false


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• Nested if…else statements– One inside another, test for multiple cases – Once a condition met, other statements are skipped– Example

• If student’s grade is greater than or equal to 90 Print “A” Else

If student’s grade is greater than or equal to 80 Print “B”

Else If student’s grade is greater than or equal to 70

Print “C” Else If student’s grade is greater than or equal to 60 Print “D”

Else Print “F”


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• Nested if…else statements (Cont.)

– Written In C++• if ( studentGrade >= 90 )

cout << "A";else if (studentGrade >= 80 ) cout << "B"; else if (studentGrade >= 70 ) cout << "C"; else if ( studentGrade >= 60 ) cout << "D"; else cout << "F";


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• Nested if…else statements (Cont.)

– Written In C++ (indented differently)• if ( studentGrade >= 90 )

cout << "A";else if (studentGrade >= 80 ) cout << "B";else if (studentGrade >= 70 ) cout << "C"; else if ( studentGrade >= 60 ) cout << "D";else cout << "F";


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• Dangling-else problem– Compiler associates else with the immediately

preceding if– Example

• if ( x > 5 ) if ( y > 5 ) cout << "x and y are > 5";else cout << "x is <= 5";

– Compiler interprets as• if ( x > 5 )

if ( y > 5 ) cout << "x and y are > 5"; else cout << "x is <= 5”;// output is incorrect


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switch Multiple-Selection Statement

•switch statement– Used for multiple selections– Tests a variable or expression

• Compared against constant integral expressions to decide on action to take

– Any combination of character constants and integer constants that evaluates to a constant integer value


Example Switch statement 54 char grade; // grade entered by user55 cout << "Enter the letter grades." << endl56 cin >> grade ;57 // determine which grade was entered 58 switch ( grade ) // switch statement nested in while59 { 60 case 'A': // grade was uppercase A 61 aCount++; // increment aCount 62 break; // necessary to exit switch 63 64 case 'B': // grade was uppercase B 65 bCount++; // increment bCount 66 break; // exit switch 67 68 case 'C': // grade was uppercase C 69 cCount++; // increment cCount 70 break; // exit switch 71 } // end switch statement

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4.7 while Repetition Statement

• Repetition statement– Action repeated while some condition remains true– Example

• int product = 3;

while ( product <= 100 ) product = 3 * product;


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Repetition Statement

•for repetition statement– Specifies counter-controlled repetition details in a single

line of code for ( initialization; loopContinuationCondition; increment )

statement;


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Fig. 5.3 | for statement header components.


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do…while Repetition Statement

•do…while statement– Similar to while statement– Tests loop-continuation after performing body of loop

• Loop body always executes at least once– Example

int product = 3; do { product = 3* product ; } while ( product <= 100);


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Conditions of if statements may be formed using relational/equality and logical operators


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Fig. 2.12 | Equality and relational operators.

Standard algebraic equality or relational operator

C++ equality or relational operator

Sample C++ condition

Meaning of C++ condition

Relational operators > x > y x is greater than y < x < y x is less than y >= x >= y x is greater than or equal to y <= x <= y x is less than or equal to y Equality operators = == x == y x is equal to y ≠ != x != y x is not equal to y


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5.8 Logical Operators

• Logical operators– Allows for more complex conditions

• Combines simple conditions into complex conditions

• C++ logical operators– && (logical AND)– || (logical OR)– ! (logical NOT)


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Fig. 5.15 | && (logical AND) operator truth table.

expression1 expression2 expression1 && expression2

false false false false true false true false false true true true


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Fig. 5.16 | || (logical OR) operator truth table.

expression1 expression2 expression1 || expression2

false false false false true true true false true true true true


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Fig. 5.17 | ! (logical negation) operator truth table.

Expression !expression

false true true false


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Fig. 2.9 | Arithmetic operators.

C++ operation C++ arithmetic operator

Algebraic expression

C++ expression

Addition + f + 7 f + 7 Subtraction - p – c p - c Multiplication * bm or b· m b * m

Division / x / y or xy

or x ÷ y x / y

Modulus % r mod s r % s


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4.11 Assignment Operators

• Assignment expression abbreviations– Addition assignment operator

• Example– c = c + 3; abbreviates to c += 3;

• Statements of the formvariable = variable operator expression;

can be rewritten asvariable operator= expression;

• Other assignment operators– d -= 4 (d = d - 4)– e *= 5 (e = e * 5)– f /= 3 (f = f / 3)– g %= 9 (g = g % 9)


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4.12 Increment and Decrement Operators

• Increment operator ++ – Increments variable by one

• Example– c++

• Decrement operator -- – Decrement variable by one

• Example– c--


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Fig. 4.20 | Increment and decrement operators.

Operator Called Sample expression Explanation

++ preincrement ++a Increment a by 1, then use the new value of a in the expression in which a resides.

++ postincrement a++ Use the current value of a in the expression in which a resides, then increment a by 1.

-- predecrement --b Decrement b by 1, then use the new value of b in the expression in which b resides.

-- postdecrement b-- Use the current value of b in the expression in which b resides, then decrement b by 1.


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4.12 Increment and Decrement Operators (Cont.)

• If c = 5, then – cout << ++c;

• c is changed to 6• Then prints out 6

– cout << c++; • Prints out 5 (cout is executed before the increment) • c then becomes 6


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Fig. 4.22 | Operator precedence for the operators encountered so far in the text.

Operators Associativity Type () left to right parentheses ++ -- static_cast< type >() left to right unary (postfix)

++ -- + - right to left unary (prefix)

* / % left to right multiplicative

+ - left to right additive

<< >> left to right insertion/extraction

< <= > >= left to right relational

== != left to right equality

?: right to left conditional

= += -= *= /= %= right to left assignment

coen 244 - 4 - control statement

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