Introducing block scheme programming March 17

Algorithm / Flow chart An algorithm or a flowchart is a step-by-step procedure for solving a particular problem, independently of the programming language. 2 A general plan for solving problems consist of Write the specification of the problem to be solved i.e. inputs, outputs Draw flowchart or write algorithm Convert flowchart (algorithm) into program code Compile the program into object code Execute the program

Flow chart basic symbols 3 Computations Input / Output Decision Start / stop Connector Flow of control

Adding the numbers 4 start read A, B, C S = A + B + C output S stop

Larger of two numbers 5 start read X, Y output X stop X > Y ? output Y stop yes no

Larger of three numbers 6 start read X, Y, Z stop X > Y ? stop yesno max > Z ? Output max Output z yesno Max = XMax = Y

7 start read N stop Count > N ? output sum no yes sum = sum + count * count sum = 0 count = 1 count = count + 1 Sum = … + N 2

8 start read N stop Count > N ? output sum no yes sum = sum + count * (count + 1) sum = 0 count = 1 count = count + 1 sum = 1 * * * 4 + … + N * (N +1)

9 start read N stop count > N ? output sum no yes prod = prod * count prod = 1 count = 1 count = count + 1 Computing factorial

10 start Read X, N stop count > N ? output sum no yes sum = prod * count term = term * X / count term = 1 prod = 1 count = 1 count = count + 1 Computing e x series up to N terms Use Taylor expansion to represent e x up to N terms.

11 start Read X, N stop term <.0001 ? output sum no yes sum = prod * count term = term * X / count term = 1 prod = 1 count = 1 count = count + 1 Computing e x series up to 4 decimal places Use Taylor expansion to represent e x up to 4 decimal places.

Do you it yourself Draw a block scheme for the algorithm that finds roots of quadratic equations ax 2 + bx + c = 0 12

Homework Draw a flowchart for the following algorithms 1.Find whether a number is prime or not. 2.Find sin(x), using the following series Hint: see problem on slides 10 and …