Check if a string is a base 16 number - c++

Question

I've been trying to solve this task, but I had no positive results.
So, my task is to check if a string is a base 16 number.
example : s="1AB", it will show YES 427
Here is my code.
#include <iostream>
#include <string.h>
using namespace std;
int power (int a, int b)
{
if(b==1) return a;
else return a*power(a,b-1);
}
void conv(char s[],int &n)
{
int S=0,i,p=0;
for(i=n-1;i>=0;i--)
{
if(s[i]>='0' && s[i]<='9')
S+=(s[i]-48) * power(16,p); //ex:s[i]='1' ==> S+=(49-49)*...
else S+=(s[i]-55) * power(16,p); //s[i]='A' ==> S+=(65-55) *...
p++;
}
}
int main()
{
int n,i,k=0;
char s[255];
cin.get(s,255);
cin.get();
n=strlen(s);
for(i=0;i<n;i++)
{
if(strchr("0123456789ABCDEF",s[i])) k++;
}
if(k==0) cout<<"not in base 16";
else{
conv(s,n); cout<<s;}
return 0;
}

Answer 1

If you want almost clean solution, you can check mine:
#include <iostream>
using namespace std;
bool IsHex(string& in) {
for (char d : in) {
if (!isxdigit(d)) return false;
}
return true;
}
int Convert(string& in) {
int val = 0;
for (char d : in) {
val = val * 16 + (isdigit(d)? d - '0' : 10 + (isupper(d)? d - 'A' : d - 'a'));
}
return val;
}
int main() {
string in;
cin >> in;
if (!IsHex(in)) cout << "Not a correct hex number" << endl;
else cout << "YES " << Convert(in) << endl;
return 0;
}
And I have made some changes in your code to make it work. You can easily find out changes.
#include <iostream>
#include <string.h>
using namespace std;
int power (int a, int b)
{
if (b == 0) return 1;
if(b==1) return a;
else return a*power(a,b-1);
}
int conv(char s[],int &n)
{
int S=0,i,p=0;
for(i=n-1;i>=0;i--)
{
if(s[i]>='0' && s[i]<='9')
S+=(s[i]-48) * power(16,p); //ex:s[i]='1' ==> S+=(49-49)*...
else S+=(s[i]-55) * power(16,p); //s[i]='A' ==> S+=(65-55) *...
p++;
}
return S;
}
int main()
{
int n,i,k=0;
char s[255];
cin.get(s,255);
cin.get();
n=strlen(s);
for(i=0;i<n;i++)
{
if(!strchr("0123456789ABCDEF",s[i])) break;
}
if(i < n) cout<<"not in base 16";
else{
cout << conv(s,n) << endl;}
return 0;
}

Answer 2

You can just use std::isxdigit, for example:
#include <cctype>
#include <string>
#include <iostream>
bool IsThisStringAHexNumber(std::string const &str)
{
for (size_t i = 0, n = str.length(); i < n; ++i)
if (!std::isxdigit(str[i]))
return false;
return true;
}
int main()
{
std::cout << std::boolalpha << IsThisStringAHexNumber("298722h2jjh") << std::endl;
std::cout << std::boolalpha << IsThisStringAHexNumber("2abc66f") << std::endl;
return 0;
}
Prints:
false
true