# write your own Atoi function

implement the function atoi. The function takes a string(str) as argument and converts it to an integer and returns it.

**Example 1:**

Input:

str = 123

Output: 123

**Example 2:**

Input:

str = 21a

Output: -1

Explanation: Output is -1 as all

characters are not digit only.

**c++ implementation with explanation:**

int atoi(string str) { //Your code here int result=0; //Stores and returns the integer converted value for str int i=0; //just a current character pointer for string int sign = 1; //multiplied at the end to result to determine if the string is +ve or -ve if(str[i]=='-') //Check the sign of string (+ or -) { sign = -1; i++; } //Now traverse the entire string and convert it into integer while(str[i]) { //If any character is not an integer then just return -1 if(!(str[i]-'0'>=0 && str[i]-'0'<=9)) return -1; //else just keep updating the result result = result*10 + str[i]-'0'; i++; } return result*sign; }

**Time Complexity:** O(n) ,where n is the length of the string