Flowcharts¶
A flowchart is a diagram that uses different shapes and arrows to show the steps in a process or how to solve a problem.
In programming, we use flowcharts to plan out algorithms, which are step-by-step instructions for solving a problem.
Symbols¶
Different shapes in a flowchart each have a special meaning.
Each shape shows a different type of step in a program.
Flow arrows¶
Flow arrows show the path the program takes through the flowchart.
They only go in one direction, which is shown by the arrowhead.
Process blocks¶
Process blocks show the steps where your code does something in order.
For example:
setting values for variables
doing calculations
running functions
They are shown as a rectangle with a short description inside.
Flows:
inflow arrows – must have at least one, but can have more than one
outflow arrows – must have one, and only one
Terminal blocks¶
Terminal blocks show where a process starts and ends.
They are drawn as rounded rectangles.
For a main program, they say “Start” or “End”
For a function, they show the function name or what value it returns
Flows:
start terminal inflow arrows – none
start terminal outflow arrows – must have one, and only one
end terminal inflow arrows – must have one, and only one
end terminal outflow arrows – none
Input/Output (IO) blocks¶
Input/Output (IO) blocks show when information moves between the real world and the program.
Input is when information goes into the program, such as:
typing on a keyboard
using a mouse
using a gamepad or joystick
recording with a camera
recording with a microphone
Output is when the computer sends information out, such as:
showing text or images on a screen
playing sound
making vibrations
printing on paper
IO blocks are drawn as parallelograms, with a short description of the input or output inside.
Flows:
inflow arrows – must have at least one, but can have more than one
outflow arrows – must have one, and only one
Decision blocks¶
Decision blocks ask a question and then split the path based on the answer.
They are drawn as a diamond, with the question written inside.
Decision blocks are the only shape that can have more than one path coming out. Each arrow should be labelled with the answer (like “yes” or “no”) that follows that path.
Flows:
inflow arrows – must have one, and only one
outflow arrows – must have at least one, but can have more than one
Additional symbols¶
In this course, we have also used two extra symbols to help show how flowcharts work:
loop indicator
function indicator
You do not have to use these symbols, but you can use them if they help make your flowcharts easier to understand.
Loop indicator¶
The loop indicator is a grey box with dashed lines.
It goes around a loop and shows which steps are repeated. It starts or ends at the decision block that checks the loop condition.
Function indicator¶
The function indicator is a red box with dashed lines.
It goes around a function. The function’s start is at the top, and the end is at the bottom.
No flow arrows should go into or out of the function indicator.
Example¶
Below is a flowchart for a number guessing game.
The game requirements are:
Generate a random number between 1 and 100
Ask the user to guess the number
If the number is incorrect, it tells the user if they guessed too high or two low
If the number is correct, it tells the user how many guesses they had.
Validate user input to ensure incorrect types cannot be entered
Only accept numbers between 1 and 100
Ask the user to play again
