c++ to_string was not declared in this scope error [Windows + Devcpp environment]

Question

I am trying to implement the Karatsuba multiplication algorithm in c++ on Windows 10 using Devcpp ide. Here is the code for the same:

#include <iostream>
#include <string>
#include <cmath>
using namespace std;

int karatsuba(int x, int y){
    string sx = to_string(x);
    string sy = to_string(y);
    int len_x = strlen(sx);
    int len_y = strlen(sy);
    if (len_x == 1 && len_y == 1)
        return x * y;
    else{
        int n = max(len_x, len_y);
        int n_by_2 = n / 2;

        int a = x / pow(10, n_by_2);
        int b = x % pow(10, n_by_2);
        int c = y / pow(10, n_by_2);
        int d = y % pow(10, n_by_2);

        int ac = karatsuba(a, c);
        int bd = karatsuba(b, d);

        int ad_plus_bc = karatsuba(a+b, c+d);
        int prod = ac * pow(10, n_by_2) + (ad_plus_bc * pow(10, n_by_2)) + bd;
        return prod;
    }
}

int main(){
    cout<<karatsuba(45, 45);
}

When I run this program I get these errors:

C:\Users\AKuro\Desktop\C++\Divide and Conquer\karatsuba.cpp In function 'int karatsuba(int, int)': 7 25 C:\Users\AKuro\Desktop\C++\Divide and Conquer\karatsuba.cpp [Error] 'to_string' was not declared in this scope

9 23 C:\Users\AKuro\Desktop\C++\Divide and Conquer\karatsuba.cpp [Error] 'strlen' was not declared in this scope

18 29 C:\Users\AKuro\Desktop\C++\Divide and Conquer\karatsuba.cpp [Error] invalid operands of types 'int' and '__gnu_cxx::__promote_2::__type {aka double}' to binary 'operator%'

20 29 C:\Users\AKuro\Desktop\C++\Divide and Conquer\karatsuba.cpp [Error] invalid operands of types 'int' and '__gnu_cxx::__promote_2::__type {aka double}' to binary 'operator%'

I tried the methods I found through Googling but none of them seem to work. Here is what I have already tried:

using std with to_string as such std::to_string

I have even tried this approach

int i = 1212;
stringstream ss;
ss << i;
string s=ss.str();

but none seems to work and I couldn't find any answer to this particular environment (Windows 10 + Devcpp). It has been really bugging me. Please if you could help me out.

What compiler options are you using? What exactly do you mean by "*none seems to work*" (any errors)? — melpomene, Apr 16 '18 at 10:21
`std::string` has `.size()` function, use it instead of `strlen` (which works only on string literals: "qwe") — R2RT, Apr 16 '18 at 10:23
Enable [c++11](https://stackoverflow.com/questions/16951376/how-to-change-mode-from-c98-mode-in-dev-c-to-a-mode-that-supports-c0x-ran) — Thomas Sablik, Apr 16 '18 at 10:25
Also be aware of rounding when using `std::pow` with integer values: https://stackoverflow.com/questions/29787310/does-pow-work-for-int-data-type-in-c — AMA, Apr 16 '18 at 10:29

score 1 · Answer 1 · answered Apr 17 '18 at 08:11

There are multiple errors here:

1) to_string() is a c++11 feature. So make sure you set -std=c++11 in your makefile or IDE.

2) strlen() is declared in cstring, not string. Better way here is to use something like int len_x = sx.size();, and similar for the other string.

3) Return type of pow() is float or double. So you need to cast it expicitly like this: int b = x % static_cast<int>(pow(10, n_by_2));. You need to do this for all expressions which use pow() and assign result to int variable. Actually, even better than casting would be to write your own simple intpow() function, which is not hard to do (it is so simple that the standard seems to have skipped it :-) ).

Thank you mahesh this really helped me out...was struggling with it for quite a while — AKuro, Apr 17 '18 at 12:13

c++ to_string was not declared in this scope error [Windows + Devcpp environment]

1 Answers1