## Code Snippet: atoi Implementation in C
### Overview
The image presents a C code snippet that implements the `atoi` function, which converts a string to an integer. It also includes a `main` function that demonstrates the usage of the `atoi` function.
### Components/Axes
* **Header:** `#include <stdio.h>`
* **Function `atoi`:**
* Input: `char *str` (a string)
* Local variables: `result` (initialized to 0), `sign` (initialized to 1)
* Logic:
* Skips leading whitespace characters (space, tab, newline, carriage return, vertical tab, form feed).
* Handles optional leading '+' or '-' sign.
* Iterates through the string as long as the characters are digits ('0' to '9').
* Calculates the integer value by multiplying the current `result` by 10 and adding the numerical value of the current digit.
* Returns the final `result` multiplied by the `sign`.
* **Function `main`:**
* Input: `int argc`, `char *argv[]` (command-line arguments)
* Logic:
* Checks if the number of command-line arguments is not equal to 2. If so, prints a usage message and returns 1.
* Calls the `atoi` function with the first command-line argument (`argv[1]`).
* Prints the parsed integer value.
* Returns 0.
### Detailed Analysis or ### Content Details
The code begins by including the standard input/output library (`stdio.h`). The `atoi` function is defined to take a character pointer `str` as input. It initializes `result` to 0 and `sign` to 1.
The first `while` loop skips any leading whitespace characters. The `if` statement checks for a leading '+' or '-' sign. If a '-' is found, the `sign` is set to -1.
The second `while` loop iterates through the string as long as the characters are digits. Inside the loop, the `result` is updated by multiplying it by 10 and adding the numerical value of the current digit (obtained by subtracting '0' from the character).
Finally, the function returns the `result` multiplied by the `sign`.
The `main` function checks if the program is called with exactly one argument. If not, it prints a usage message. Otherwise, it calls `atoi` to convert the argument to an integer and prints the result.
**Code Transcription:**
