Modify binary search to perform only one test inside the loop instead of two. Move any necessary checks outside the loop.

1. Reduce the number of tests inside the loop.

2. Add required checks outside the loop.

3. Measure and compare execution time with the original.

Analyze whether the optimization improves performance.

Write a function `escape(s, t)` that converts special characters (e.g., newline, tab) in `t` into visible escape sequences (e.g., `\n`, `\t`) and stores the result in `s`. Use a `switch` statement.

Write another function to perform the reverse operation, converting escape sequences back into their actual characters.

1. Implement `escape(s, t)` using a `switch` statement.

2. Implement the reverse function.

3. Test both functions with various input cases.

The functions should correctly transform strings between escaped and unescaped representations.

Write a function `expand(s1, s2)` that expands shorthand notations like `a-z` in `s1` into the full sequence `abc...xyz` in `s2`. The function should handle:

- Both uppercase and lowercase letters.

- Digit ranges like `0-9`.

- Edge cases such as `a-b-c`, `a-z0-9`, and `-a-z`, ensuring leading or trailing `-` is treated literally.

1. Parse `s1` and identify valid shorthand ranges.

2. Expand recognized patterns into their full sequences.

3. Handle edge cases correctly.

4. Store the result in `s2` and test with various inputs.

The function should accurately expand shorthand notations while correctly handling edge cases.

In two's complement representation, the standard `itoa` function fails for the most negative number (`-(2^(wordsize-1))`). This happens because negating this value exceeds the range of positive numbers representable in the same number of bits.

Modify `itoa` to correctly handle this edge case on any machine.

1. Identify why `itoa` fails for the largest negative number.

2. Implement a fix that works across different word sizes.

3. Ensure correctness by testing with various inputs, including the edge case.

The modified `itoa` function should correctly convert the most negative number to a string representation, regardless of system architecture.

Write the function `itob(n, s, b)` that converts the integer `n` into a base `b` character representation in the string `s`. In particular, `itob(n, s, 16)` should format `s` as a hexadecimal integer in `s`.

1. Identify the logic needed to convert an integer `n` into a string representation in a given base `b`.

2. Implement the conversion for bases 2 through 16, mapping numbers to the correct characters (`0-9` for digits and `a-f` for hexadecimal).

3. Handle both positive and negative numbers, ensuring that negative values are properly represented.

4. Reverse the string since the remainder of divisions is stored in reverse order.

5. Add a null terminator at the end of the string.

The function `itob` should correctly convert integers into strings representing the number in any base from 2 to 16, with correct handling of both positive and negative integers.

Write a version of `itoa` that accepts three arguments instead of two. The third argument is a minimum field width; the converted number must be padded with blanks on the left if necessary to make it wide enough.

1. Modify the `itoa` function to accept three arguments: the integer `n`, the character array `s`, and the minimum field width `width`.

2. Implement the logic to convert the integer `n` into a string representation.

3. Ensure that the string is padded with blank spaces on the left if its length is less than the specified minimum field width `width`.

4. Handle both positive and negative numbers, ensuring that negative values are represented correctly and the padding does not overwrite the negative sign.

5. Ensure that the converted string is null-terminated.

The modified `itoa` function should correctly convert the integer `n` into a string, ensuring that if the converted number is shorter than the specified field width, it is padded with blank spaces on the left.

Write the function `strindex(s, t)` which returns the position of the rightmost occurrence of the string `t` in the string `s`, or `-1` if there is none.

1. Implement the function `strindex` that takes two string arguments, `s` and `t`.

2. Search for the rightmost occurrence of string `t` in string `s`.

3. Return the position (index) of the first character of the rightmost occurrence of `t` in `s`. If `t` does not exist in `s`, return `-1`.

4. Ensure that the function works for all valid input strings, including edge cases where `t` is empty or not found.

The function `strindex` should correctly return the index of the rightmost occurrence of `t` in `s`, or `-1` if `t` is not found.

An alternate organization uses `getline` to read an entire input line; this makes `getch` and `ungetch` unnecessary. Revise the calculator to use `getline` for input instead of `getch` and `ungetch`.

1. Replace the usage of `getch` and `ungetch` with `getline` to read entire lines of input.

2. Modify the input parsing logic to handle input as a complete line, instead of reading one character at a time.

3. Ensure that `getline` can properly read input of varying lengths, handling large inputs and input with spaces correctly.

4. Update the tokenizer or expression parsing logic to work with entire lines of input rather than processing characters individually.

5. Remove any code related to managing a character buffer (e.g., `buf` and `bufp`) that was previously used with `getch` and `ungetch`.

6. Test the modified calculator to ensure it behaves correctly with this new input handling approach, including handling different input sizes and formats.

The calculator should function correctly with `getline` used to read entire input lines. It should no longer rely on `getch` and `ungetch`, and the logic should be updated to handle complete lines of input. The calculator should properly parse and evaluate expressions from the input lines.

Modify `getop` so that it doesn't need to use `ungetch`. Use an internal static variable to store the pushed-back character instead.

1. Analyze the current implementation of `getop` and identify where it relies on `ungetch` to push characters back.

2. Replace the use of `ungetch` with an internal static variable within `getop`. This static variable will store the last pushed-back character.

3. Implement logic within `getop` to check if the internal static variable has a stored character. If it does, return that character first before reading new input.

4. If the internal static variable is empty, proceed with reading a new character from the input.

5. Ensure that once the internal static variable is used, it is reset to avoid incorrect behavior during future calls to `getop`.

6. Test the modified `getop` to ensure it correctly handles input and pushed-back characters, without requiring `ungetch`.

The modified `getop` function should no longer need to rely on `ungetch` for pushing characters back. Instead, it should use an internal static variable to store and retrieve a pushed-back character. The function should behave correctly, with input being handled efficiently and without errors.

Adapt the ideas of `printd` to write a recursive version of `itoa`. This version should convert an integer into a string by calling a recursive routine.

1. Understand how `itoa` works by converting an integer into a string using iteration. The recursive version will rely on similar principles but will use recursion instead of iteration.

2. Implement a recursive function that converts the integer to a string. The base case for the recursion should handle when the number is zero, and the recursive case should reduce the problem size by dividing the number by 10.

3. In the recursive function, handle the sign of the number by checking if it's negative and appropriately adding the minus sign when necessary.

4. Build the string from the least significant digit to the most significant one. This can be done by recursively processing the digits in reverse order.

5. Once the recursive function is complete, ensure that the string is properly null-terminated and handles edge cases such as zero and negative numbers.

The recursive `itoa` function should correctly convert an integer into a string, with each recursive call processing one digit at a time. The function should properly handle both positive and negative integers and return a correctly formatted string