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# Convert string to integer without using any in-built functions

• Last Updated : 31 Aug, 2020

Given a string str, the task is to convert the given string into the number without using any inbuilt function.

Examples:

Input: str = “985632”
Output: 985632
Explanation:
Given input is in string form and returned output is in integer form.

Input: str = “123”
Output: 123
Explanation:
Given input is in string form and returned output is in integer form.

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: The idea is to use the ASCII value of the digits from 0 to 9 start from 48 – 57.
Therefore, to change the numeric character to an integer subtract 48 from the ASCII value of the character will given the corresponding digit for the given character.

Below is the implementation of the above approach:

## C++

 `// C++ program for tha above approach ``#include  ``using` `namespace` `std; `` ` `// Function to convert string to ``// integer without using functions ``void` `convert(string s) ``{ ``    ``// Initialize a variable ``    ``int` `num = 0; ``    ``int` `n = s.length(); `` ` `    ``// Iterate till length of the string ``    ``for` `(``int` `i = 0; i < n; i++) `` ` `        ``// Subtract 48 from the current digit ``        ``num = num * 10 + (``int``(s[i]) - 48); `` ` `    ``// Print the answer ``    ``cout << num; ``} `` ` `// Driver Code ``int` `main() ``{ ``    ``// Given string of number ``    ``char` `s[] = ``"123"``; `` ` `    ``// Function Call ``    ``convert(s); ``    ``return` `0; ``} `

## C

 `// C program for the above approach ``#include  ``#include  `` ` `// Function to convert string to ``// integer without using functions ``void` `convert(``char` `s[]) ``{ ``    ``// Initialize a variable ``    ``int` `num = 0; ``    ``int` `n = ``strlen``(s); `` ` `    ``// Iterate till length of the string ``    ``for` `(``int` `i = 0; i < n; i++) `` ` `        ``// Subtract 48 from the current digit ``        ``num = num * 10 + (s[i] - 48); `` ` `    ``// Print the answer ``    ``printf``(``"%d"``, num); ``} `` ` `// Driver Code ``int` `main() ``{ ``    ``// Given string of number ``    ``char` `s[] = ``"123"``; `` ` `    ``// Function Call ``    ``convert(s); ``    ``return` `0; ``} `

## Java

 `// Java program for the above approach ``class` `GFG{ `` ` `// Function to convert string to ``// integer without using functions ``public` `static` `void` `convert(String s) ``{ ``     ` `    ``// Initialize a variable ``    ``int` `num = ``0``; ``    ``int` `n = s.length(); `` ` `    ``// Iterate till length of the string ``    ``for``(``int` `i = ``0``; i < n; i++) `` ` `        ``// Subtract 48 from the current digit ``        ``num = num * ``10` `+ ((``int``)s.charAt(i) - ``48``); `` ` `    ``// Print the answer ``    ``System.out.print(num); ``} `` ` `// Driver code ``public` `static` `void` `main(String[] args) ``{ ``    ``// Given string of number ``    ``String s = ``"123"``; `` ` `    ``// Function Call ``    ``convert(s); ``} ``} `` ` `// This code is contributed by divyeshrabadiya07 `

## Python3

 `# Python3 program for the above approach `` ` `# Function to convert string to ``# integer without using functions ``def` `convert(s): `` ` `    ``# Initialize a variable ``    ``num ``=` `0``    ``n ``=` `len``(s) `` ` `    ``# Iterate till length of the string ``    ``for` `i ``in` `s: `` ` `        ``# Subtract 48 from the current digit ``        ``num ``=` `num ``*` `10` `+` `(``ord``(i) ``-` `48``) `` ` `    ``# Print the answer ``    ``print``(num) `` ` `# Driver code ``if` `__name__ ``=``=` `'__main__'``: `` ` `    ``# Given string of number ``    ``s ``=` `"123"`` ` `    ``# Function Call ``    ``convert(s) `` ` `# This code is contributed by Shivam Singh `

## C#

 `// C# program for the above approach ``using` `System;`` ` `class` `GFG{`` ` `// Function to convert string to ``// integer without using functions ``public` `static` `void` `convert(``string` `s) ``{ ``     ` `    ``// Initialize a variable ``    ``int` `num = 0; ``    ``int` `n = s.Length; `` ` `    ``// Iterate till length of the string ``    ``for``(``int` `i = 0; i < n; i++) `` ` `        ``// Subtract 48 from the current digit ``        ``num = num * 10 + ((``int``)s[i] - 48); `` ` `    ``// Print the answer ``    ``Console.Write(num); ``} `` ` `// Driver code``public` `static` `void` `Main(``string``[] args)``{``     ` `    ``// Given string of number ``    ``string` `s = ``"123"``; `` ` `    ``// Function call ``    ``convert(s); ``}``}`` ` `// This code is contributed by rock_cool`
Output:
```123
```

Time Complexity: O(N), where N is the length of the given string.
Auxiliary Space: O(1)

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