How it could be optimized [C++]? - c++

Question

I was doing some C++ "homework" and I've made an exercise which says the following:
Input
The input consists of a sequence of characters, which include exclusively lowercase letters, spaces and newlines.
[Table with letter-number values]
Output
Your program must print the total value of the message, computed as the sum of the value of all its letters.
And I've done this!:
#include<iostream>
using namespace std;
int main() {
char v;
int val = 0;
while(cin >> v){
if (v == 'a' or v == 'e') val += 1;
if (v == 'o' or v == 's') val += 2;
if (v == 'd' or v == 'i' or v == 'n' or v == 'r') val += 3;
if (v == 'c' or v == 'l' or v == 't' or v == 'u') val += 4;
if (v == 'm' or v == 'p') val += 5;
if (v == 'k' or v == 'w') val += 7;
if (v == 'b' or v == 'f' or v == 'g' or v == 'h') val += 6;
if (v == 'j' or v == 'q' or v == 'v' or v == 'x' or v == 'y' or v == 'z') val += 6;
}
cout << val << endl;
}
Example:
INPUT:
is a chinese wok
OUTPUT:
42
(I end the While loop by pressing Ctrl+D, which is how the evaluation web does.)
Which is a pretty simple and working solution but...
I was wandering if there's any way of doing this without a bunch of "if's". Gotta say, I can't include anything else than iostream.
Thanks!

Answer 1

As another answer indicates, you can use a map. That's the most compact way of writing this algorithm, but it will not necessarily result in best performance.
There are two more ways that I can think of. A somewhat better way is with a switch statement, like this:
int get_increment( char v )
{
switch( v )
{
case 'a': case 'e':
return 1;
case 'o': case 's':
return 2;
case 'd': case 'i': case 'n': case 'r':
return 3;
case 'c': case 'l': case 't': case 'u':
return 4;
case 'm': case 'p':
return 5;
case 'k': case 'b': case 'f': case 'g': case 'h':
return 6;
case 'w':
return 7;
case 'j': case 'q': case 'v': case 'x': case 'y': case 'z':
return 6;
default:
return 0; //not a letter!
}
}
but if you want the maximum performance, then a lookup table is the way to go.
Here is how to initialize the lookup table:
int increments[256];
for( int i = 0; i < 256; i++ )
increments[i] = 0;
for( char c = 'a'; c <= 'z'; c++ )
increments[c] = get_increment( c );
and then here is how to use it:
val += increments[(unsigned char)v];
Note: the cast of v to unsigned char is not strictly speaking necessary, if v is only going to contain letters. But it will save your program from a crash if characters in your architecture are signed, (and they usually are,) and v happens to contain a negative value.