Display the appropriate message as per the colour of signal at the road crossing.

Question

Accepted Answer

> [!TLDR]
> Map each signal colour to its message with an if–elif–else ladder on the input string, normalised with upper() so the comparison is case-insensitive.

**The idea.** The traffic signal is a *multi-way selection over string values*: three known colours, each with its own message, plus a default for anything unrecognised. An if–elif ladder with string equality tests expresses this directly. Because the user may type red, Red or RED, we normalise the input once with upper() instead of testing every spelling.

**Program**

```python
colour = input("Enter the colour of the signal: ")
colour = colour.upper()          # case-insensitive matching

if colour == "RED":
    print("STOP")
elif colour == "YELLOW":
    print("WAIT")
elif colour == "GREEN":
    print("GO")
else:
    print("Invalid colour. Please enter RED, YELLOW or GREEN.")
```

**Sample runs**

```text
Enter the colour of the signal: red
STOP
```

```text
Enter the colour of the signal: Green
GO
```

```text
Enter the colour of the signal: blue
Invalid colour. Please enter RED, YELLOW or GREEN.
``` …

Q.Display the appropriate message as per the colour of signal at the road crossing.

Concept understanding — Conditional Logic

Conditional Logic: From Intuition to Precision

The Intuition: When Is Your Promise Broken?

The Precise Statement

Common Patterns in Conditional Logic

$P$	$Q$	$P \rightarrow Q$
T	T	T
T	F	F
F	T	T
F	F	T

Q.Display the appropriate message as per the colour of signal at the road crossing.

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