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C++ Program to Convert String to Integer
  • Last Updated : 01 May, 2020

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
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// 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;
}

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Output:

12345


How to do using library functions?

Please refer Converting Strings to Numbers in C/C++ for library methods.

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