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C++ Program to Convert String to Integer

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  • Difficulty Level : Basic
  • Last Updated : 21 Jun, 2022
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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 <bits/stdc++.h>
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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