Inputting 30-something and -Ex42 with an output of 30 and Ex42 - c++

Question

I can't understand how I would do this.
The input will be:
3
13894
30-something
-Ex42
and the output needs to be:
13894
30
Ex42
The main assignment is to make a function that converts a duodecimal number into the decimal format. I have figured that part out and don't need help with it. I've basically cut out all the code surrounding the duodecimal conversion and just included the stuff I can't figure out.
#include <iostream>
#include <string>
#include <iomanip>
using namespace std;
int to_decimal(const string& str);
int main () {
string str; // Initializes string str for input
cin.ignore (256, '\n'); //ignores the 3 from the input
while (getline(cin, str)) {
//runs str through to_decimal and outputs
cout << to_decimal(str) << endl;
}
}
int to_decimal(const string& str) {
int f = 0;
string localString; // Initialize local string variable
//sets local string to the same as inputted string
localString = str; //used for local string erasing
//This is the idea I have been working on and I cant figure it out
for (unsigned x = 0; x < localString.length(); x++) {
f = localString.at(x);
if (isdigit(f)) {
} else if (f == 'E'){
} else if (f == 'e') {
} else if (f == 'X') {
} else if (f == 'x') {
} else if (f == '-') {
} else if (f == ' ') {
} else {
f = localString.length() - x;
localString.erase(x, f);
break;
}
}
}

Answer 1

I am a bit confused. You say that you need to convert duodecimal numbers to decimal, however in your sample output only the line that has Ex is converted, yet 30-something stays 30, as if it is not converted - and 30 in duodecimal is 36 in decimal. Same for the number 13894.
Assuming that you really want to convert all of the lines from duodecimal to decimal, you can base your solution on the standard library function std::stoi() which can convert a string from most number bases up to 36. It requires that the digits bigger than 9 are encoded using the letters in alphabetic order - A to Z. So you need to simply convert all you x to a and all you e to b. Example:
int to_decimal(const string& str) {
bool foundDigit = false;
std::string transformedString;
for (auto c : str) {
if (std::isdigit(c) || c == 'E' || c =='e' || c == 'X' || c == 'x') {
foundDigit = true;
// If needed, convert the character.
if (c == 'E' || c == 'e') {
c = 'b';
} else if (c == 'X' || c == 'x') {
c = 'a';
}
transformedString += c;
} else if (foundDigit) {
// Skip everything to the end of the line, if we've already found some digits
break;
}
}
return std::stoi(transformedString, 0, 12);
}

Answer 2

If you just want to extract the characters and then do the conversion yourself, then you can do something like this:
#include <iostream>
#include <string>
#include <sstream>
bool isNumber(const char c)
{
switch (c) {
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
case '0':
case 'e':
case 'E':
case 'x':
case 'X':
case '-':
return true;
default:
return false;
}
}
std::string getNumber(std::istream& in)
{
std::stringstream s;
for (char c;in.get(c);)
{
if (isNumber(c)) {
s << c;
break;
}
}
for (char c;in.get(c);)
{
if (!isNumber(c))
break;
s << c;
}
return s.str();
}
int main()
{
std::string bla = "3\n13894\n 30-something\n-Ex42\n";
std::stringstream klaf{ bla };
for (std::string s;(s = getNumber(klaf)) != "";) //<- use a local stringstream as input to test
//for (std::string s;(s = getNumber(std::cin)) != "";) //<- use std::cin for input
{
std::cout << s << '\n';
}
}
This outputs:
3
13894
30-
e
-Ex42
So, not exactly what you were after, but it should at least get you a starting point to improve from. For example, you may want to remove - from isNumber and then change to logic in getNumber to only accept it as the first character in a new number.