CC213 Programming Applications Week #2

Control Structures • Control structures –control the flow of execution in a program or function. • Three basic control structures:  Sequential Flow - this is written as a group of statements bracketed by { and }where one statement follows another.  Selection control structure - this chooses between multiple statements to execute based on some condition.  Repetition – this structure executes a block of code multiple times.

C

Y

N

Y

C N

2

C control structures • Selection if if . . . else switch

• Repetition for loop while loop do . . . while loop 3

Conditions • A program chooses among alternative statements by testing the values of variables.  0 means false  Any non-zero integer means true, Usually, we’ll use 1 as true. if (a>=b) printf(“a is larger”); else printf(“b is larger”); • Condition - an expression that establishes a criterion for either executing or skipping a group of statements  a>=b is a condition that determines which printf statement we execute. 4

Relational and Equality Operators • Most conditions that we use to perform comparisons will have one of these forms:    

variable relational-operator variable e.g. a < b variable relational-operator constant e.g. a > 3 variable equality-operator variable e.g. a == b variable equality-operator constant e.g. a != 10

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Relational and Equality Operators Operator

Meaning

Type




greater than

relational

=

greater than or equal to

relational

==

equal to

equality

!=

not equal to

equality 6

Logical Operators • logical expressions - expressions that use conditional statements and logical operators.  && (and)  A && B is true if and only if both A and B are true  || (or)  A || B is true if either A or B are true  ! (not)  !(condition) is true if condition is false, and false if condition is true  This is called the logical complement or negation • Example  (salary < 10000) || (dependents > 5)  (temperature > 90.0) && (humidity > 90)  !(temperature > 90.0) 7

Truth Table && Operator A

B

A && B

False (zero)

False (zero)

False (zero)

False (zero)

True (non-zero)

False (zero)

True (non-zero)

False (zero)

False (zero)

True (non-zero)

True (non-zero)

True (non-zero) 8

Truth Table || Operator A

B

A || B

False (zero)

False (zero)

False (zero)

False (zero)

True (non-zero)

True (non-zero)

True (non-zero)

False (zero)

True (non-zero)

True (non-zero)

True (non-zero)

True (non-zero) 9

Operator Table ! Operator

A

!A

False (zero)

True (non-zero)

True (non-zero)

False (zero)

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Remember! • && operator yields a true result only when both its operands are true. • || operator yields a false result only when both its operands are false.

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If-Else Syntax if ( Expression ) StatementA else StatementB

NOTE: StatementA and StatementB each can be a single statement, a null statement, or a block. 12

Example: mail order Write a program to calculate the total price of a certain purchase. There is a discount and shipping cost: The discount rate is 25% and the shipping is 10.00 if purchase is over 100.00.

Otherwise, The discount rate is 15% and the shipping is 5.00 pounds.

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Note: These braces cannot be omitted if ( purchase > 100.00 ) { discountRate = .25 ; shipCost = 10.00 ; } else { discountRate = .15 ; shipCost = 5.00 ; } totalBill = purchase * (1.0 - discountRate) + shipCost ; 14

Switch statement Used to select one of several alternatives BASED on the value of a single variable. This variable may be an int or a char but NOT a float ( or double).

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Example char grade ; printf(“Enter your letter grade: “); scanf(“%c”, &grade); switch ( grade ) { case „A‟ : printf(“ Excellent Job”); break; case „B‟ : printf ( “ Very Good “); break; case „C‟ : printf(“ Not bad “); break; case „F‟ : printf(“Failing”); break; default : printf(“ Wrong Input “); } 16

Example: Light bulbs Write a program to ask the user for the brightness of a light bulb (in Watts), and print out the expected lifetime: Brightness Lifetime in hours 25 2500 40, 60 1000 75, 100 750 otherwise 0 17

int bright ; printf(“Enter the bulb brightness: “); scanf(“%d”, &bright); switch ( bright ) { case 25 : printf(“ Expected Lifetime is 2500 hours”); break; case 40 : case 60 : printf ( “Expected Lifetime is 1000 hours “); break; case 75 : case 100 : printf(“Expected Lifetime is 750 hours “); break; default : printf(“Wrong Input “); } 18

What is a loop? • A loop is to execute a set of instructions repeatedly until a particular condition is being satisfied . • That is, you can execute particular statements more than once in a controlled fashion

• Statements are executed as long as some condition remains true 19

Two Types of Loops count controlled loops repeat a specified number of times

event-controlled loops some condition within the loop body changes and this causes the repetetion to stop

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While Statement SYNTAX

while ( Expression ) { . . . }

/*loop body */

NOTE: Loop body can be a single null statement, or a block.

statement, a 21

Parts of a While Loop • Every while loop will always contain three main elements: – Priming: initialize your variables. – Testing: test against some known condition. – Updating: update the variable that is tested. 22

Count-controlled Loop int count ; 1. Priming

count = 4;

/* initialize loop variable */ 2. Test Condition

while (count > 0) { printf(“ %d \n ”,count ) ; count -- ; } printf( “Done” ) ;

/* test expression */ /* repeated action */

/*update loop variable */ 3. Update

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Computing Sum 100

• If we want to compute , we need to go i  1+2+3+...+100 i 1 • We can use a while loop. /* computes the sum: 1 + 2 + 3 + ....+ 100 */ #include int main(void) { int sum =0, i = 1; while (i