Thread: convert string into integer using recursion

hi, can someone give me an idea on how to convert string to integer using array
for example

string n = '123';
int c;

cout<<c;

and will display 123.

what i think of is 123 divide by 10 or the second idea tat i have is

for example: string s = 123

|1|2|3|
---------
0 1 2

and

s[n-1] = 3
+
s[n-2] = 2 * 10
+
s[n-3] = 1 * 100
=
123

how can i start with?

Code:

int stringConIntRec(string number)
{
        if(number.length() == 0)
                 return 0;
        else
        {
           ???????
            ???????
         }
}

Code:

firstchar * 10 ^ depth + recursion(restofstring);

depth can be tracked with length of string.

Are you required to do it that way?

Normally in C++ you'd use stringstream:

Code:

#include <string>
#include <sstream>
int main()
{
    std::string s("123");
    int i;
    std::stringstream stoi(s);
    stoi >> i;  //voila
    return 0;
}

hi Tonto, can u descrive what does '^' mean in your code please? sorry i am newbie of c++

this is my solution and seems like got some error... being looking and thinking but couldnt get it correct. can some one list the error..?

Code:

int convertRec(string num)
{
    int y;
    
    if(num.length()==0)
        return num;
    else
    {
        int depth = num.length();
        int position = 0;
        int s = 4;
        
        y = (num[position] * 10 ^ depth) + convertRec(num.substr(depth-s, depth-10));
        s--;
    }
    return y;
}

>> 10 ^ depth
Don't actually use ^. That doesn't mean to the power of in C++. Perhaps pow() is what you want.

the power()? you mean power of deth?

Code:

int convertRec(string num)
{
    int y;
    
    if(num.length()==0)
        return 0;
    else
    {
        int depth = num.length();
        int position = 0;
        int s = 4;
        
        y = pow(num[position] * 10, depth) + convertRec(num.substr(depth-s, depth-10));
        s--;
    }
    return y;
}

is this wat you mea DAVED

On each iteration, multiply the current value by 10 and add the next.

Code:

int stoi (string &s)
{
	int  num = 0;
	int  i   = 0;
	bool neg = false;

	if (s[0] == '-') {
		neg = true;
		i++;
	}
	for (; i < s.length(); i++) {
		if (s[i] >= '0' && s[i] <= '9')
			num = num*10 + (s[i] - '0');
		else
			return -1;
	}
	if (neg)
		return -num;
	return num;
}

hi everyone, thank you for helping me but i really need to stick with recursion from converting string into integer.

really appreciate all effort....

hope can get some idea from others again...i am working on it as well...

first you must have a function which converts character 1 to 9 to integer 1 to 9;

try subtracting 48 to char but first you must store it to an integer variable

Code:

// assume you name this as num() function
char s[n];
int x=char s[n];
int z=x-48;
return z;

then you can apply your idea:

[tag]
|1|2|3|
---------
0 1 2

and

s[n-1] = 3
+
s[n-2] = 2 * 10
+
s[n-3] = 1 * 100
=
123
[/tag]

you need to do a program which first start a the first element(assume s[0]) which keeps on incrementing until it hits the end (s[strlen(s)]), and about the "x10" problem you must do a power fuction like this:

Code:

 

int power(int n){ //n is the number nth of the element (i.e. s[1] here n=1) 

int x;

for(x=0;x<n;x++){

int z=z*10; (can be z*=10)
}
return z;

using this functions you can now create a program that answers your problem recursively. (^^ sorry can't make the program right now but hope this helps)