Char seperated by a decimal into a double c++ [closed] - c++

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I am passing a string variable (std::string) and iterating through the string character by character. Whenever I run into a decimal, I want to combine the previous position on the string (i.e 2) and the next position in the string (i.e 5) into a double. So how would I go about making the char 2, char . , char 5 into one whole value (2.5)?
std::double x;
std::string varibleName = "4 5 7 2.5";
for (int i = 0; i < variableName.length(); i++) // iterates through variableName
{
if (variableName[i] == '.'){ // if the current position of the iteration is a decimal, I want to grab the char before the decimal and the char after the decimal so I can combine all three positions of the string making it 2.5 and not 25.
}
}

Answer 1

Well, you are wildly overthinking it. The C++ library provides std::stof, std::stod, std::stold that does exactly what you want. Convert a string like "2.5" to a float, double or long double, e.g.
#include <iostream>
int main (void) {
std::string s = "2.5";
double d = std::stod(s);
std::cout << d << "\n";
}
Example Use/Output
$ ./bin/stodex
2.5
Look things over and let me know if you have further overthinking questions.

Answer 2

Note that giving an example, code snips, and error logs make troubleshooting a lot easier :)
It sound like you have some input like "2.1" and need to convert it to a double like 2.1?
If that is the case you can use the <cstdlib> atof function.
Example:
/* atof example: sine calculator */
#include <stdio.h> /* printf, fgets */
#include <stdlib.h> /* atof */
#include <math.h> /* sin */
int main ()
{
double n;
char buffer[256];
printf ("Enter degrees: ");
fgets (buffer,256,stdin);
n = atof (buffer);
printf ("You entered %s which is a double like %f\n" , buffer, n);
return 0;
}