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3. Developing the solution: Design a detailed algorithm and choose appropriate tools and technologies. It is
always recommended to first write an algorithm and draw a flowchart for solving a problem and then only
write the program. This translates analysis into a practical, actionable plan.
4. Coding and implementation: This is the last step where every instruction of an algorithm is converted into
a computer understandable instruction by using the syntax and semantic of a specific computer language.
Control Structures
Control structures are a set of instructions that control the flow of instructions in a program. It is a programming
tool that determines the order of execution of the statements in any programming language. There are three
different types of control structures: sequential flow, selection flow, and repetition flow.
Let us learn about these in detail.
Sequential Flow
In sequential flow, the statements are placed one after the other and the flow of execution occurs starting from line
1, line 2 and so on with a top-down approach. It is the default flow followed in any programming language. For
example, the steps for calculating the percentage of any student by taking as an input marks of English, Science,
Maths are as follows:
Step 1 Start
Step 2 Input Eng, Science, Math
Step 3 Total = Eng+Science+Math
Step 4 Percentage = (Total / Maximum_Marks) * 100
Step 5 Display Percentage
Step 6 Stop
Selection Flow
Selection flow is also known as branching control as the flow of control branches based on a condition. A
condition evaluates to either TRUE or FALSE. In the case of TRUE, the flow of control follows the set of instructions
written for True. In case it is FALSE, then it follows the other route. For example, consider the scenario where an
award is given only if the percentage is more than 90:
Step 1 Start
Step 2 Input Eng,Science, Math
Step 3 Total= Eng+Science+Math
Step 4 Percentage = (Total / Maximum_Marks) * 100
Step 5 Display Percentage
Step 6 If Percentage> 90 then
Display "Award given"
Step 7 else
Display "No award"
Step 8 Stop
Repetition Flow
Repetition flow, also known as a loop, repeats a set of instructions a number of times based on a condition. For
example, if we wish to repeat the above steps of calculating percentage for 10 students then we use the concept
of repetition.
Introduction to Python 359

