C++ program to "Convert String to it's corresponding Integer" using Recursion

In this program we'll learn How to convert a string into into corresponding integer value.
Example:
To convert string "1234" to its integer value 1234.

#include <iostream>

#include<string.h>

#include<math.h>

using namespace std;

int StrToInt(char S[],int j,int i,int a,int b)

{

    if(S[i]=='\0')

    {

        return b;

    }

        a=S[i]-'0';

        b=a*(pow(10,j))+StrToInt(S,j-1,i+1,a,b);

    return b;

}

int main()

{

    char S[50];

    cin>>S;

    int j=strlen(S);

    int y=StrToInt(S,j-1,0,0,0);

    cout<<y;

    return 0;

}