string conversion c++ - c++

Question

I have a string and the first element is for example 'a'. I already declared a variable called a ( so int a=1 for example). My question now is, how can I convert the whole string to numbers (a=1,b=2,c=3,...z=26)? Example:
string str="hello"; this has to be changed to "85121215" and then changed to 85121215.

Answer 1

// transformation itself doesn't care what encoding we use
std::string transform_string(std::string const &in, std::function<int(char)> op)
{
std::ostringstream out;
std::transform(in.begin(), in.end(),
std::ostream_iterator<int>(out),
op);
return out.str();
}
// the per-character mapping is easy to isolate
int ascii_az_map(char ch)
{
if (ch < 'a' || ch > 'z') {
std::ostringstream error;
error << "character '" << ch << "'=" << (int)ch
<< " not in range a-z";
throw std::out_of_range(error.str());
}
return 1 + ch - 'a';
}
// so we can support other encodings if necessary
// NB. ebdic_to_ascii isn't actually implemented here
int ebcdic_az_map(char ch)
{
return ascii_az_map(ebcdic_to_ascii(ch));
}
// and even detect the platform encoding automatically (w/ thanks to Phresnel)
// (you can still explicitly select a non-native encoding if you want)
int default_az_map(char ch)
{
#if ('b'-'a' == 1) && ('j' - 'i' == 1)
return ascii_az_map(ch);
#elif ('j'-'i' == 8)
return ebcdic_az_map(ch);
#else
#error "unknown character encoding"
#endif
}
// use as:
std::string str = "hello";
std::string trans = transform_string(str, ascii_az_map);
// OR ... transform_string(str, ebcdic_az_map);
Note that since the per-character mapping is completely isolated, it's really easy to change the mapping to a lookup table, support different encodings etc.

Answer 2

Your definition is a bit small:
"hello" = "85121215
h = 8
e = 5
l = 12
o = 15
I assume you mean that
a = 1
b = 2
...
z = 26
in which case it is not that hard:
std::string meh_conv(char c) {
switch(c) { // (or `switch(tolower(c))` and save some typing)
case 'a': case 'A': return "1";
case 'b': case 'B': return "2";
....
case 'z': case 'Z': return "26";
....
// insert other special characters here
}
throw std::range_error("meh");
}
std::string meh_conv(std::string const &src) {
std::string dest;
for (const auto c : s)
dest += meh_conv(c);
return dest;
}
or use std::transform():
#include <algorithm>
std::string dest;
std::transform (src.begin(), src.end(), back_inserter(dest),
meh_conv)
(doesn't work for different incoming and outgoing types, at least not as is)
Addendum.
You possibly want to parametrize the replacement map:
std::map<char, std::string> repl;
repl['a'] = repl['A'] = "0";
repl[' '] = " ";
std::string src = "hello";
std::string dest;
for (const auto c : src) dest += repl[c];

Answer 3

I wrote you a simple example. It creates a map what contains the a-1, b-2, c-3 ... pairs. Then concatenate the values using a stringstream:
#include <iostream>
#include <map>
#include <sstream>
int main()
{
std::string str = "abc";
std::map<char,int> dictionary;
int n = 1;
for(char c='a'; c<='z'; c++)
dictionary.insert(std::pair<char,int>(c,n++));
//EDIT if you want uppercase characters too:
n=1;
for(char c='A'; c<='Z'; c++)
dictionary.insert(std::pair<char,int>(c,n++));
std::stringstream strstream;
for(int i=0; i<str.size(); i++)
strstream<<dictionary[str[i]];
std::string numbers = strstream.str();
std::cout<<numbers;
return 0;
}
C++ experts probably going to kill me for this solution, but it works ;)

Answer 4

Easy Approach,
you can find mod of char with 96 (ASCII value before a), as result it will always give you values in range 1-26.
int value;
string s;
cin>>s;
for(int i=0; i<s.size();i++){
value = s[j]%96;
cout<<value<<endl;
}