C++ Program to Convert String to Integer

• Difficulty Level : Easy
• Last Updated : 21 Jun, 2022

Given a string of digits, the task is to convert the string to an integer. Examples:

```Input : str = "12345"
Output : 12345

Input : str = "876538";
Output : 876538

Input : str = "0028";
Output : 28```

CPP

 `// C++ program to convert String into Integer``#include ``using` `namespace` `std;` `// function for converting string to integer``int` `stringTointeger(string str)``{``    ``int` `temp = 0;``    ``for` `(``int` `i = 0; i < str.length(); i++) {` `        ``// Since ASCII value of character from '0'``        ``// to '9' are contiguous. So if we subtract``        ``// '0' from ASCII value of a digit, we get``        ``// the integer value of the digit.``        ``temp = temp * 10 + (str[i] - ``'0'``);``    ``}``    ``return` `temp;``}` `// Driver code``int` `main()``{``    ``string str = ``"12345"``;``    ``int` `num = stringTointeger(str);``    ``cout << num;``    ``return` `0;``}`

Output:

`12345`

Time Complexity: O(|str|)

Auxiliary Space: O(1)

How to do using library functions? Please refer Converting Strings to Numbers in C/C++ for library methods.

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