« String to integer recursively

Problem

Write a recursive function to convert a given string into the number it represents. That is input will be a numeric string that contains only numbers, you need to convert the string into corresponding integer and return the answer.

Input format :

Numeric string S (string, Eg. "1234")

Output format :

Corresponding integer N (int, Eg. 1234)

Constraints :

0 <= |S| <= 9

where |S| represents length of string S.

Sample Input 1 :

00001231

Sample Output 1 :

1231

Sample Input 2 :

12567

Sample Output 2 :

12567

Solution

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1#include <iostream>
2#include <iomanip>
3#include <algorithm>
4#include <string>
5#include <cstring>
6#include <vector>
7#include <cmath>
8#include <map>
9#include <climits>
10// climits for INT_MIN
11#include <unordered_map>
12using namespace std;
13
14int length(char input[])
15{
16    int len = 0;
17    for (int i = 0; input[i] != '\0'; i++)
18    {
19        len++;
20    }
21    return len;
22}
23
24int stringToNumber(char input[], int len)
25{
26    if (len == 1)
27    {
28        return (input[0] - '0');
29    }
30    int x = stringToNumber(input + 1, len - 1);
31    x = x + (pow(10, len - 1) * (input[0] - '0'));
32    return x;
33}
34
35int stringToNumber(char input[])
36{
37    int len = length(input);
38    int x = stringToNumber(input, len);
39    return x;
40}
41
42int main()
43{
44    char input[50];
45    cin >> input;
46    cout << stringToNumber(input) << endl;
47    return 0;
48}