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Function Details : atoi

intatoi(const char * str) ;

Return Type : int

Integer type (typically 4 bytes, -2,147,483,648 to 2,147,483,647)
Read about return values of atoi function .

1st Parameter Type : const char *

Pointer to read-only string

1st Parameter

Pointer to a null-terminated string representing an integer value

Read more about parameters of atoi in parameters section
The atoifunction in C language Converts a string to an integer.
It skips any whitespace characters at the beginning of the string, then takes an optional plus or minus sign followed by as many base-10 digits as possible, and interprets them as a numerical value. The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function.
Important: atoi function does not recognize decimal point as it , but rather treats it as any other non-digit character and breaks the loop.

To Summarize the Workflow:
  1. 1.
    Takes a string (like "123") as input.
  2. 2.
    Scans the string, ignoring leading whitespace.
  3. 3.
    If plus or minus sign is present before digits begin- processes it as a sign.
  4. 4.
    In case no sign found-sets result to positive as default
  5. 5.
    Starts looping over following characters. In case those represent digits-processes digits.
  6. 6.
    Stops at the first non-digit character (like a letter or symbol).
  7. 7.
    Returns the integer value of the processed digits (e.g., 123).
  8. 8.
    If the string doesn’t start with a valid number, it returns 0.


Start

Receive input string

Is string NULL?

Return 0

Initialize variables

Skip leading whitespace

Check for sign

Set sign = -1

Increment index

Is digit?

Update result

Break loop

Increment index

Apply sign

Return result

End

Yes

No

Negative

Other

Yes

No





Read more about return type and value ofatoi function in return section.
The atoifunction takes 1 parameter:
  • •
    const char * `str`: Pointer to a null-terminated string representing an integer value
Converts the initial portion of a string to an `int` value, interpreting the content as a decimal integer.
The atoi function return value :
  • Returns the converted integer value
  • If no valid conversion could be performed, it returns 0

Output

This example demonstrates the basic usage of the `atoi` function with different input strings, including a positive number, a negative number with leading whitespace, a number followed by non-numeric characters, and an invalid input.