Control Structures Week 3

2.1 Introduction -Representation of the theory and principles of structured programming. Demonstration of for, while,do…whil e and switch statements 2

while Repetition Structure 3

Repetition structure – Action repeated while some condition remains true – Psuedocode while there are more money in my pocket Buy coca cola – while loop repeated until condition becomes false Example int product = 2; while ( product <= 1000 ) product = 2 * product; 4

The while Repetition Structure Flowchart of while loop 5 product <= 1000 product = 2 * product true false

Formulating Algorithms (Counter- Controlled Repetition) Counter-controlled repetition – Loop repeated until counter reaches certain value Definite repetition – Number of repetitions known Example A class of ten students took a quiz. The grades (integers in the range 0 to 100) for this quiz are available to you. Determine the class average on the quiz. 6

Formulating Algorithms (Counter- Controlled Repetition) Pseudocode for example: Set total to zero Set grade counter to one While grade counter is less than or equal to ten Input the next grade Add the grade into the total Add one to the grade counter Set the class average to the total divided by ten Print the class average Next: C++ code for this example 7

8 1 // Fig. 2.7: fig02_07.cpp 2 // Class average program with counter-controlled repetition. 3 #include 4 5 using std::cout; 6 using std::cin; 7 using std::endl; 8 9 // function main begins program execution 10 int main() 11 { 12 int total; // sum of grades input by user 13 int gradeCounter; // number of grade to be entered next 14 int grade; // grade value 15 int average; // average of grades // initialization phase 18 total = 0; // initialize total 19 gradeCounter = 1; // initialize loop counter 20

9 21 // processing phase 22 while ( gradeCounter <= 10 ) { // loop 10 times 23 cout << "Enter grade: "; // prompt for input 24 cin >> grade; // read grade from user 25 total = total + grade; // add grade to total 26 gradeCounter = gradeCounter + 1; // increment counter 27 } // termination phase 30 average = total / 10; // integer division // display result 33 cout << "Class average is " << average << endl; return 0; // indicate program ended successfully } // end function main Enter grade: 98 Enter grade: 76 Enter grade: 71 Enter grade: 87 Enter grade: 83 Enter grade: 90 Enter grade: 57 Enter grade: 79 Enter grade: 82 Enter grade: 94 Class average is 81 The counter gets incremented each time the loop executes. Eventually, the counter causes the loop to end.

Essentials of Counter-Controlled Repetition Counter-controlled repetition requires 1. the name 2. initial value 3. loop – continuation 4. increment/decrement

Counter-controlled repetition example 1. Names 1 2. Initial value Loop-continuation condition 4 4. Increment

for Repetition Statement The while statement can be used to implement any counter-controlled loop. for repetition statement specifies the counter-controlled repetition details in a single line of code.

for Repetition Statement example

Examples Using the for Statement Vary the control variable from 1 to 100 in increments of 1. for ( int i = 1; i <= 100; i++ ) Vary the control variable from 100 down to 1 in increments of -1 (that is, decrements of 1). for ( int i = 100; i >= 1; i-- )

Examples Using the for Statement Vary the control variable from 7 to 77 in steps of 7. for ( int i = 7; i <= 77; i += 7 ) Vary the control variable from 20 down to 2 in steps of -2. for ( int i = 20; i >= 2; i -= 2 )

Summing integers with the for statement.

do...while Repetition Statement Similar to the while statement Tests the loop-continuation condition after the loop body executes, therefore, the loop body always executes at least once do { statement } while ( condition );

do...while repetition statement

break and continue Statements C++ provides statements break and continue to alter the flow of control This section discusses how to use break in a repetition statement

break Statement when executed in a while, for, do...while or switch statement, causes immediate exit from that statement Program execution continues with the next statement

break statement exiting a for statement.

continue Statement when executed in a while, for or do...while statement, skips the remaining statements in the body of that statement and proceeds with the next iteration of the loop In while and do...while statements, the loop- continuation test evaluates immediately after the continue statement executes. In the for statement, the increment expression executes, then the loop-continuation test evaluates.

Logical Operators logical operators are used to form more complex conditions by combining simple conditions. The logical operators are: - && (logical AND) - || (logical OR) - ! (logical NOT, also called logical negation).

Logical AND (&&) Operator When we wish to ensure that two conditions are both TRUE before we choose a certain path of execution if ( gender == 1 && age >= 65 ) seniorFemales++;

&& (logical AND) operator truth table - The table shows all four possible combinations of false and true

Logical OR (||) Operator When we wish to ensure at some point in a program that either or both of two conditions are TRUE before we choose a certain path of execution if ( ( semesterAverage >= 90 ) || ( finalExam >= 90 ) ) cout << "Student grade is A" << endl;

|| (logical OR) operator truth table

Logical Negation (!) Operator the ! (logical NOT, also called logical negation) operator enable a programmer to "reverse" the meaning of a condition the preceding if statement also can be written as follows ! (logical negation) operator truth table

Confusing Equality (==) and Assignment (=) Operators Confusing do not cause syntax errors Using operator == for assignment and using operator = for equality are logic errors. suppose we intend to write but we accidentally write

THANK YOU FOR YOUR ATTENTION