Program 8-3: Write a program to input a string from the user and print it in the reverse order without creating a new string.

Question

Accepted Answer

> [!TLDR]
> Use negative indexing to PRINT the existing string backwards — iterate i over range(-1, -len(st)-1, -1) and print st[i] with end='' — so no reversed copy is ever created.

**Idea.** The constraint "without creating a new string" rules out slicing tricks like st[::-1] (that builds a reversed copy). But printing needs no new string at all: Python's negative indices already address the string from the back — st[-1] is the last character, st[-2] the second last, … st[-len(st)] the first. Walking i from -1 down to -len(st) prints the original string's characters in reverse order.

```python
st = input("Enter a string: ")
print("The string in reverse order is:")
for i in range(-1, -len(st) - 1, -1):
    print(st[i], end='')
print()   # final newline
```

Key lines:
- `range(-1, -len(st) - 1, -1)` — start at -1, step -1, stop *before* -len(st)-1, i.e. the last value produced is -len(st). For a 5-character string: -1, -2, -3, -4, -5.
- `print(st[i], end='')` — end='' suppresses print's default newline so the characters appear joined on one line.

**Trace** for st = "Hello" (len = 5):

| i | st[i] | printed so far |
|---|-------|----------------|
| -1 | o | o |
| -2 | l | ol |
| -3 | l | oll |
| -4 | e | olle |
| -5 | H | olleH | …

Q.Program 8-3: Write a program to input a string from the user and print it in the reverse order without creating a new string.

Concept understanding — String Reversal In Place

String Reversal In Place

The Intuition

The Precise Statement

Why It Works

A Concrete Example

Q.Program 8-3: Write a program to input a string from the user and print it in the reverse order without creating a new string.

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