Indeed, the expression time_step here is a string, sorry about that (Maybe a string concatenation would work?)
Here is the beginning of the code, that you might find useful to see :
/* This program works as a pipe between Geochemist's Workbench and MATLAB */
#include "RC_helper.h"
#include <iostream>
#include <string>
// #include <stdio.h>
using namespace std;
//void pipe(string &, string &, string &);
void main(string &mass_W, string &time_step, string &temp)
{
char* script1[] =
{
"reset",
//"time begin = 0 seconds, end = " + time_step + " seconds",
//"T = " + temp + " K",
"SiO2(aq) = 1 umolal",
"react 5000 g Quartz",
"kinetic Quartz rate_con = 2.e-15 surface = 1000",
"go",
""
};
Thank you