C++ Program To Write Your Own atoi()
The atoi() function in C takes a string (which represents an integer) as an argument and returns its value of type int. So basically the function is used to convert a string argument to an integer.
int atoi(const char strn)
Parameters: The function accepts one parameter strn which refers to the string argument that is needed to be converted into its integer equivalent.
Return Value: If strn is a valid input, then the function returns the equivalent integer number for the passed string number. If no valid conversion takes place, then the function returns zero.
String value = 12546 Integer value = 12546 String value = GeeksforGeeks Integer value = 0
Time Complexity : O(N)
Auxiliary Space : O(1) , as no extra space is needed.
Now let’s understand various ways in which one can create their own atoi() function supported by various conditions:
Approach 1: Following is a simple implementation of conversion without considering any special case.
- Initialize the result as 0.
- Start from the first character and update result for every character.
- For every character update the answer as result = result * 10 + (s[i] – ‘0’)
Approach 2: This implementation handles the negative numbers. If the first character is ‘-‘ then store the sign as negative and then convert the rest of the string to number using the previous approach while multiplying sign with it.
Approach 3: This implementation handles various type of errors. If str is NULL or str contains non-numeric characters then return 0 as the number is not valid.
Approach 4: Four corner cases needs to be handled:
- Discards all leading whitespaces
- Sign of the number
- Invalid input
To remove the leading whitespaces run a loop until a character of the digit is reached. If the number is greater than or equal to INT_MAX/10. Then return INT_MAX if the sign is positive and return INT_MIN if the sign is negative. The other cases are handled in previous approaches.
Below is the implementation of the above approach:
Complexity Analysis for all the above Approaches:
- Time Complexity: O(n).
Only one traversal of string is needed.
- Space Complexity: O(1).
As no extra space is required.
Write your won atof() that takes a string (which represents an floating point value) as an argument and returns its value as double.
Please refer complete article on Write your own atoi() for more details!
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