atoi.c

#include <cs50.h>
#include <ctype.h>
#include <math.h>
#include <stdio.h>
#include <string.h>

int convert(string input);

int main(void)
{
    string input = get_string("Enter a positive integer: ");

    for (int i = 0, n = strlen(input); i < n; i++)
    {
        if (!isdigit(input[i]))
        {
            printf("Invalid Input!\n");
            return 1;
        }
    }

    // Convert string to int
    printf("%i\n", convert(input));
}

int convert(string input)
{
    // TODO
    int length=strlen(input);

    //base case recursive
    if (length==1)
    {
        return input[0]-'0'; // ascii code 0=48, so -0 to get the number's ascii code
    }

    // recursive base

    char last_digit= input [length -1];
    int coverted_last_digit= last_digit - '0';

    input[length-1]='\0';

    //Return this value plus 10 times the integer value of the new shortened string
    return coverted_last_digit + 10* convert(input);



}