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Loops in Flowcharts

Repeat steps with a decision and an arrow that goes back up — counter-controlled and condition-controlled loops.

Iteration: Repeating Steps

A loop repeats steps. In a flowchart, a loop is a decision (diamond) plus an arrow that goes back up to an earlier step. There is no separate loop symbol: if a question asks which shape shows a loop, the answer is the diamond . The decision decides whether to go round again or to leave the loop. Every loop needs three things: 1 Start value — set before the loop (for example number = 1). 2 Condition — checked in the decision (number <= 9?). 3 Change — something inside the loop that moves towards the end (number = number + 2). Without it, the loop never ends.

Output the odd numbers from 1 to 9

Read this flowchart as text

The arrow on the left goes back up to the decision. When the condition becomes No, the loop ends.

Sometimes you do not know how many times to repeat. At the shop, the cashier enters prices one by one and types 0 when the customer has no more items. The 0 is a sentinel (rogue) value that ends the loop.

Add up prices until 0 is entered

Read this flowchart as text

The first INPUT is before the loop; the second is at the end of the loop, just before going back to the decision.

Check your answer: multiples of 5 up to 30

Read this flowchart as text

Practice

A loop's decision is "count < 10?" but nothing inside the loop changes count. What happens?

Iteration: Repeating Steps

A loop repeats steps. In a flowchart, a loop is a decision (diamond) plus an arrow that goes back up to an earlier step. There is no separate loop symbol: if a question asks which shape shows a loop, the answer is the diamond . The decision decides whether to go round again or to leave the loop. Every loop needs three things: 1 Start value — set before the loop (for example number = 1). 2 Condition — checked in the decision (number <= 9?). 3 Change — something inside the loop that moves towards the end (number = number + 2). Without it, the loop never ends.

A Counter-Controlled Loop: Odd Numbers 1 to 9

Output the odd numbers from 1 to 9

Read this flowchart as text

The arrow on the left goes back up to the decision. When the condition becomes No, the loop ends.

A Condition-Controlled Loop: Keep Adding Prices

Sometimes you do not know how many times to repeat. At the shop, the cashier enters prices one by one and types 0 when the customer has no more items. The 0 is a sentinel (rogue) value that ends the loop.

Add up prices until 0 is entered

Read this flowchart as text

The first INPUT is before the loop; the second is at the end of the loop, just before going back to the decision.

Types of Loop

Check your answer: multiples of 5 up to 30

Read this flowchart as text

Practice

A loop's decision is "count < 10?" but nothing inside the loop changes count. What happens?