Array help! - Dev Articles

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October 30th, 2009, 12:33 AM

spazamatic2

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Array help!

I need to ask the user to input a bunch of letters until a '-' symbol is entered. I then need to total up how many letters of each letter there are and find a percentage presented in 2 columns.
eg. input addfhb-
letter frequency
a 0.17
b 0.17
c 0
d 0.33
e 0
f 0.17
g 0
h 0.17
.
.
.
I am not sure where to get started on my code and how I would intialize or define an array. Thank you

October 30th, 2009, 08:27 AM

MaHuJa

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Normally, I say "don't use array, use vector". In this case, however, using either of them is not really appropriate.

In this particular use case, I suggest using a map instead. It is a far better tool for the job.

cpp Code:

Original - cpp Code

#include <iostream>
#include <map>
 
using namespace std;
 
int main() {
    map<char,int> table;
    char c;
    int totalcount;
    cin >> c;
    while (c!='-') {
        totalcount++;
        table[c]++;
        cin >> c;
    }
    // Iterator interface to maps, reads only the ones for which there actually is any data.
    map<char,int>::iterator it;
    float total = totalcount;
    for (it=table.begin(); it!=table.end(); it++) {
        cout << it->first << '\t' << it->second/total << '\n';
    }
}

No data exists for the letters that haven't been entered, so it won't show them.

I don't recommend it, but without the iterators you can still do

Code:

const char letters[]="abcdefghij";
for (int j=0; j<strlen(letters); j++)
    cout << letters[j] << '\t' << table[letters[j]]/(float)total << '\n';
}

which will, as a side effect, create the data for each letter it hasn't yet seen.

If you absolutely have to use arrays, such as because you're using a compiler from the early 80s or a teacher for the same period, create an array
int table[256];
and make sure to set each of them to 0 first. Then you can use it similarly to the map with the non-iterator version of the read.

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