Control Structures

Control Structures • Repetition • or • Iteration • or • Looping • Part I

Open the salesperson file Print heading on form Skip 3 lines Read the first record Print salesperson’s name SequencePrint out a sales report

yes no sales > quota bonus = 0 bonus=sales*.01 Decision (selection, branching)

Option=1 Option=2 Option=3 Option=4 Switch (Multiple Decision)

No More? Yes Comm = Sales*.02 Calculate Pay Print Check Repetition (iteration, looping)

The for Statement • Syntax for (initialize; expression; alter) statement Example: for (cnt=1; cnt < 7; cnt++) { cout << “Yankees are #1\n”; cout << “They’ll win the Series!\n”; }next statement *

The for Statement • used as a counting loop • semicolons separate the items • items 1 and 2 are statements (end with ;) • your may declare variable and initialize it ex. for (int cnt = 1; cnt < 7; cnt++) • performs the same functions as the while

A Simple Example int num;cout << "NUMBER SQUARE CUBE\n" << "------ ------ ----\n"; • for (num = 1; num < 11; num++){ cout << setw(3) << num << " " << setw(3) << num * num << " " << setw(4) << num * num * num << "\n";} *

for Statement Examples • for (k = 1; k <= n; k = k + 1) k = k * k; for (j = 2; k % j == 0; j = j + 1){ cout << j << “ is a divisor of “ << k << ‘\n’; sum = sum + j;} *

for Statement Examples • Not Valid:for (j = 0, j < n, j = j + 3) // semicolons needed • for (j = 0; j < n) // three parts needed

Example 2: j = 1; sum = 0; for ( ; j <= 10; ) sum = sum + j; Example 3: j = 1; sum = 0; for ( ; ; ) { sum = sum + j; j++; cout << "\n" << sum;} for -- Null Expressions • Example 1: j = 1; sum = 0; for ( ; j <= 10; j = j + 1) sum = sum + j; * * *

if ... while... while ... while ... Nested Loops When a decision or control structure is contained within another decision or control sturcture, the inner one is said to be nested. You may have repetition within decision and vice versa. * *

Nested Loops - Ex.1 • Example • int y,z; • for (y = 5; y > 0; y--) • { cout << "\nAli R."; • cout << “**”; • } for (z = 1; z < 3; z++)cout <<"\tVic R.\t"; *

Nested Loops - Ex.1 Output Ali R.Vic R. Vic R. ** • Ali R.Vic R. Vic R. **Ali R.Vic R. Vic R. **Ali R.Vic R. Vic R. **Ali R.Vic R. Vic R. ** *

Nested Loops - Ex.1 Execution1 2 3 4 5 4 5 4 6 2 3 4 5 4 5 4 6 2 3 4 5 4 5 4 6 2 3 4 5 4 5 4 6 2 3 4 5 4 5 4 6 2 7 • 1 int y,z; • 2for (y = 5; y > 0; y--) • 3 { cout << "\nAli R."; • 4for (z = 1; z < 3; z++)5 cout <<"\tVic R.\t"; • 6 cout << “**“;7 } *

Nested Loops - Ex. 2 1 for (exper =1; exper<=4; exper=exper +1)2{ cout << "\tScores for experiment "<< exper <<":\n";3 total = 0.0; • 4 for (trial = 1; trial <=6; trial = trial +1)5 { cout << "Enter result of trial " << trial <<" : ";6 cin >> score;7 total = total + score;8 } • 9 avg = total/(trial-1);10 cout << "Average for experiment "<< exper11 << " is “<< setprecision(4)<< avg<< "\n\n";12 } * *

The while Statement • Syntax while (expression) statement Example: count = 1; while (count <= 10) { cout << “Yankees are #1\n”; count = count + 1; } next statement *

for vs. while • cnt = 1; • while (cnt < 7) • { cout << … • cnt++; • } for (cnt = 1; cnt < 7; cnt++) {cout << … } *

The while Statement • Syntax while (expression) statement • a loop control variable is evaluated in the expression • the loop statements contain the lines executed each time the loop repeats

0 or False Exit the while Test the expression 1 or True loop statements to execute The while Statement

Something to Note Note Note... • count = 1; while (count <= 10) { cout << “Yankees are #1\n”; cout << “and will win the series\n”; } next statement *

The while Statement • loop control variable is initialized before while statement • evaluation or test is performed within the expression • the body may contain any number of statements, including branches and other loops • the control variable is changed during loop execution in order to exit loop • the statement immediately after the while is executed upon exiting * * * * *

A Simple Example • int num;cout << "NUMBER SQUARE CUBE\n" << "------ ------ ----\n"; num = 1; while (num < 11){ cout << setw(3) << num << " " << setw(3) << num * num << " " << setw(4) << num * num * num <<‘\n’; num++; // increment num} * * *

Another Example • double celsius, fahren;cout << "CELSIUS FAHRENHEIT\n" << "------- ----------\n"; celsius = 5; // starting Celsius value while (celsius <= 50){ fahren = (9.0/5.0) * celsius + 32.0; cout << setw(4) << celsius << setiosflags(ios::showpoint) << setw(13) << setprecision(2) << fahren << '\n'; celsius = celsius + 5;} * * *

Still Another Example • year = 1;deprec = 4000;endyr = 28000;accum_depreci = 0; • while (year <= 7){ endyr = endyr - deprec; accum_depreci = accum_depreci + deprec; cout << year << deprec << endyr << accum_depreci << "\n"; • year = year + 1;} * * *

Problem Solving:Finding the Largest Value The program asks for the number of items in the list. Checks to see if that number is positive. Gets user input. Assigns the largest to variable max. * * * *

int count = 0, n = 0; double max = 0, x = 0; • cout << "The maximum value will be computed.\n"; • cout << "How many numbers do you wish to enter? "; cin >> n; • while (n <= 0) { cout << "\nERROR: Positive integer required.\n\n”; cout << "How many numbers to enter? "; cin >> n; } cout << “Enter a real number: “;cin >> x;max = x; // first value to max * * * *

while (count++ < (n-1)) // first n accepted above{ cout << “Enter a real number: “; cin >> x; if (max < x) max = x;} • cout << “Maximum value: “ << max << “\n”;} • OutputThe maximum value will be computed. How many numbers do you wish to enter? 4 Enter a real number: 1.01 Enter a real number: -3 • Enter a real number: 2.2 Enter a real number: 7.07000 Maximum value: 7.07 * * *

Closer look at a counter: cout << “Enter “ << n << … cin >> x;max = x;// count = 0 1while (count++ < (n-1))2{ 3cout << “LOOP number: “ 4cin >> x;5if (max < x)6max = x;7} loopcount n executed 1 5 1 2 2 3 3 4 4 5 *

Running Totals // count =1 • while (count <=4){ cout << “Enter a number: “; cin >> num; total = total + num; cout << “The total is “ << total; count++;} *

Bowling Team Example • A bowling team consists of five players each of whom bowls three games. Write a program that allows the user to enter each players scores and displays the players average. The team average is displayed at the end. • First write a plan.

Bowling Team Plan • display instructions • for - players • for - games • I/O scores • sum scores • average scores • display scores • sum player averages • team average • display team average

Common Errors Improper braces in nested structures Using = in place of == != versus == This changes the logic, be especially careful when used with && or || infinite loops: != versus && versus || *

The End - part I • The End The End The End The End The End The End The End The End The End The End The End The End

Control Structures