counting letter occurences in a string

hey guys, i have an extra credit assignment that wants me to count how many times each letter occurs in a string, i'm not sure how to get started:

heres the description, it doens't seem like it will be real difficult, but i'm having trouble getting started

Write a function that counts the occurance of each letters occurance in a string.
The function should recieve as formal paramater only an array of characters.
Use the following header :


void count(const char myStr[])


For the function call

count("ABcaBadd*eekjdfefdeg,TTew44Tt")

Only the following output should be produced :
The letter A occurs 3 times
The letter B occurs 2 times
The letter C occurs 1 times
The letter D occurs 4 times
The letter E occurs 5 times
The letter F occurs 2 times
The letter G occurs 1 times
The letter J occurs 1 times
The letter K occurs 1 times
The letter T occurs 4 times
The letter W occurs 1 times

Do you know maps? That's what I would use.

If you haven't learned those yet you can also use an array and find a way to convert a character to an index of the array. The array would then hold the count of each character. As you loop through the characters in the input string, you just convert the character to an index and increment that index's count.

i do not konw maps .. so yea .. that indexing method seems like it would work better. would i need to write something that places A into index 1 and B into index 2 and so on .. and then count each index?

Except that the keys of the maps would be sequential (chars), so you could just use an array.

The mapping isn't difficult either: you do know that char's are an integral type?

May-be this can enlighten you:

Code:

---

#include<iostream>

int main()
{
    for (unsigned i = 32; i != 128; ++i)
        std::cout << i << " maps to " << (char)i << '\n';
}

---

I'd use a std::map, but this should work almost as well as a map:

Code:

---

unsigned int asciiTable[256] = { 0 };

---

>> would i need to write something that places A into index 1 and B into index 2 and so on ..
Yes, although I would put 'A' into index 0 since arrays start at 0.

It would be a simple formula that works on all characters (and you might need a separate forumla for upper versus lower case characters). You could also use a big array like cpjust suggested so that you don't need to come up with that formula, but you'd have to do a little extra work later to output only the counts of the characters.

how do i assign a letter to an index in an array? how do i assign a to index 0?

You have to come up with a formula to convert it. anon gave a hint earlier, a char variable is really just an integer code for a certain letter, so you need to convert that integer code to the integer index.

Quote:

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Originally Posted by Daved

You could also use a big array like cpjust suggested so that you don't need to come up with that formula, but you'd have to do a little extra work later to output only the counts of the characters.

---

Actually, since the specific letters that you want to count are passed to the function, it should be as simple as using this in a loop:

Code:

---

unsigned int count = asciiTable[ myStr[i] ];

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The output should be in alphabetic order, so I don't think that would work exactly right.

Quote:

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Originally Posted by Daved

The output should be in alphabetic order, so I don't think that would work exactly right.

---

The moment somebody mentions "alphabetical" we're already locked in to a specific encoding. Without knowing the encoding there is no way to define what "alphabetical" even means. So if an encoding is to be assumed, we might as well assume ASCII, and use the "subtract 'A' " trick.

Quote:

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Originally Posted by Daved

The output should be in alphabetic order, so I don't think that would work exactly right.

---

I didn't see Alphabetic Order as one of the requirements; only that they need to be in the array of characters passed to the function.

>> I didn't see Alphabetic Order as one of the requirements
The expected output is listed in the original post, and it is in alphabetical order.

>> So if an encoding is to be assumed, we might as well assume ASCII, and use the "subtract 'A' " trick.
Yes, that's the idea that we're hoping the OP figures out. This appears to be a simple homework assignment, I doubt it's necessary to handle character sets other than ASCII.

Quote:

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Originally Posted by Daved

>> I didn't see Alphabetic Order as one of the requirements
The expected output is listed in the original post, and it is in alphabetical order.

---

OK, for some reason I thought the input string was the list of characters to search for...
In that case, the example also counts letters without regard to case, so you'd have to use toupper() or tolower() on each character first before counting them.

Also, to really impress the teacher, you could use the std::count_if() function.

alrite .. well don't i want to do something like this ..

*Index letter A to 0*
*Index letter B to 1*
*Index letter C to 2*
*so on, so on until Z*

then

*count Index 0 *
*count Index 1*
*count Index 2*
*etc, etc, etc*

then

*cout << count index 0*
*cout << count index 1*
*So on, so on, etc, etc*

that is how i am thinking of this in my head .. is that the correct way of accomplishing this project?

There is more than one way to solve the problem, but that method sounds good to me. One thing to note is that the middle part can be done more easily. Instead of counting characters based on the index, go through the input string and increment the count of each character in that string.

this is pretty well covered in your anagram program thread.

i'm having a hard time figuring out how to write the code to do that, also .. the code in my anagram i'm finding it difficult to see waht i can relate from the anagram code to this code

Quote:

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Originally Posted by pjr5043

i'm finding it difficult to see waht i can relate from the anagram code to this code

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this is exactly how the code worked that both todd burch and i posted.

his is more directly applicable to this problem, whereas mine counted strictly alphabetical characters.

if you understood how those anagram programs worked, you should understand this one already.

alrite .. i'll have to look at them an analyze them more

alrite guys .. i reallly need some help with this, i tried looking at the previous code i had for my anagram program, but i cannot understand it at all.

here is an update:

the teacher wants me to use this function: "void count(const char myStr[])"
and she wants me to call this: "count("ABcaBadd*eekjdfefdeg,TTew44Tt")"
the output needs to be this: "The letter A occurs 3 times
The letter B occurs 2 times
The letter C occurs 1 times
The letter D occurs 4 times
The letter E occurs 5 times
The letter F occurs 2 times
The letter G occurs 1 times
The letter J occurs 1 times
The letter K occurs 1 times
The letter T occurs 4 times
The letter W occurs 1 times"

here is my code so far

Code:

---

#include <iostream>
#include <cctype>
#include <cstring>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

using namespace std;




int main (){

        const char myStr[]="ABcaBadd*eekjdfefdeg,TTew44Tt";

int a=0;
int i=0;
        for(i=0; myStr1[i] !='\0'; i++){
                if (isalpha (myStr1[i])){
                myStr2[a]=myStr1[i];
                        a++;
                               
                }       
        }
myStr2[a]='\0';
        cout  << myStr2 << endl;






                return 0;
}

---

i need to get rid of myStr2 because the char needs to be const, so after that all i have done is eliminate all spaces and punctuation and just filter out the letters. I don't know what i should write in the function, and then what i need to write in the main function.

again i looked at the prevoius advice that was given, and the code as well, but i am not familair with any of that, i am on a very basic level, i'm really looking for some help, this is an extra credit assignment as well that would really help out my grade

Just use std::map if you are allowed to. Once you get the string comparison down the rest of the work is done for you.

i don't know what a std::map is .. i don't know how it works or how to use it

there is always google
http://www.google.com/search?q=man+s...2+Google&meta=

http://www.google.com/search?hl=en&q...om&btnG=Search

yea but i never learned that in my class .. i need to use only things i've learned .. i believe get.line will be part of this program

I don't see where mystr2 is even defined. That code isn't compiling, is it?

You need to figure out how to convert the character myStr1[i] into an index a. It's basically converting the character code for 'a' into the number 0 (or 1 if you prefer 1 for some reason). I think it is safe to assume that the characters 'a' through 'z' will all be in order, so you can use that information for this problem.

Focus on that part of the task.

daved, mystr2 isn't declared .. and that program doenst compile. the reason its in there is because originally i was going to index a new string with just the alpha characters, but i found out i can only use one const char ..

i'm really confused on these 2 points:

1. what to write in my void funciton
2. what to write in my main function

and i don't know if this is any help but i know how to index one string to another, but i don't know how to index letters to a number and then have them counted

>> but i found out i can only use one const char
What do you mean by this? Can you give an example. It doesn't sound correct to me. You can have more than one string. Your second array does not have to be a parameter, it can be declared inside the function.

In this case, myStr2 isn't a string at all, assuming that it is the array you are using to count the number of times a character is found. It should be an array that holds counts and counts are not characters, they are numbers.

Now, as for your questions, you need to figure out what code to put in the void count(const char myStr[]) and what not to, right? Well, look at the signature of the function. It takes only a string. That has to be the input string, right? So the code inside count has to go through the entire string and count the characters. As far as main goes, you just need to call the count function. Your assignment gives an example of how to do that. I don't think you need anything else in there, all the important code goes inside count.

>> but i don't know how to index letters to a number
You figure this out. It is not that hard. There are lots of hints in this thread.

what i meant for myStr2 was that .. visual studio wont let me convert a const char to char .. so i couldnt index mystr to mystr2

this is what i have ... where do i got from here?!?!? guys if you could be a little more straightforward it would help me a ton .. all i do is get more confused when i hear a bunch of idfferent wayt on how to do things without ever seeing how to do it

Code:

---

#include <iostream>
#include <string>
using namespace std;

int main (){
       
        const char myStr[]="ABcaBadd*eekjdfefdeg,TTew44Tt";
        int count[256];

        for(int i=0; myStr[i] !='\0'; i++){
                if (isalpha (myStr[i]))
                cout <<  myStr[i];
       
        }
/*
        for(int i=0; myStr[i] !='\0'; i++)
                cout << "the letter: "<< i << " occured " << count[i] << " times"<< endl;

*/       

               



        return 0;

}

---

You tell us how you plan on solving the problem. Yes, there are lots of different hints here, but if you understand them, then it is not too confusing.

You have a start. You are outputting the characters in the string that are alphabetic characters.

These are the steps I would follow:

1. Create an empty void count(const char myStr[]) function that does nothing. Compile and make sure the code compiles.
2. Call that function from main the way the assignment demonstrates. Make sure that compiles.
3. Take your code that you have now that checks isalpha and add it to the count function. Make sure that compiles. Then run it and make sure you get something you expect.
4. Now comes the harder part. How do you define the count array. First, don't call it count, because the name of the function has to be count (according to the assignment). So give it a different name. In your current code you made it an array of int. That is good, because the counts will be ints. You specified 256 as the size. That can work but is not the only way. Do you know why you picked 256?
5. The answer to the previous question will tell you what to do here. Instead of using cout to output the character at myStr[i] you need to increment the proper count. How you do it depends on how you intend to solve the problem. Work on understanding your solution in English (not code), and if you get stuck then ask about that part here.

ok i have this code .. i just want to change one thing, instead of entering a string .. i'd like to have this be the default string "ABcaBadd*eekjdfefdeg,TTew44Tt"

Code:

---

#include <iostream>
#include <cctype>
using namespace std;

//counts how many each character shows

void count(const char myStr[]){
        for (int x = 97; x < 123; x++){
                int count1 = 0;
                for (int i =0; myStr[i] != '\0' ; i++){
                        if (myStr[i] == (char)x){
                                count1++;
                        }
                }
                if (count1 != 0)
                cout << (char)x << " appears " << count1 << " times\n";
        }
}

int main(){

        char phrase1[500];

        cout << "What is your String?\n";
        cin.getline (phrase1, 500);

        const int x=500;
        char myarray[x];

        int c = 0;
        //takes each char from the string and check to see if it is both
        // not a space and is a alphabetical char
        for(int i = 0; phrase1[i] != '\0'; i++){
                if (isalpha(phrase1[i])){
                        myarray[c]=tolower(phrase1[i]);
                        c++;
                }
        }
        //reassigns null terminator to the end of the array
        myarray[c]= '\0';

        count(myarray);

        return 0;
}

---

You can initialize phrase1 with whatever you want and skip the input part.

BTW, what is 97 and 123?

Quote:

---

Originally Posted by pjr5043

//counts how many each character shows
void count(const char myStr[]){
for (int x = 97; x < 123; x++){
int count1 = 0;
for (int i =0; myStr[i] != '\0' ; i++){
if (myStr[i] == (char)x){
count1++;
}
}
if (count1 != 0)
cout << (char)x << " appears " << count1 << " times\n";
}
}
[/CODE]

---

This can be done in a better way!!!

Code:

---

void count(const char myStr[]){
    declare an array of 26 integers to store the count of each alphabet

    initialize the array variables to zero   

    loop until you reach the end of myStr[]
        if current variable in myStr[] is an alphabet
            increment the corresponding index in the integer array
   
    loop through the integer array and print the values in each index
}

---

cheers
maverix

thank you for your help .. and daved the 97 and 123 was so taht it only counts 26 times .. the amount of letter that are in the alphabet i guess, i recieved that from another student because i was having so much trouble with the program

Thanks. I figured you didn't write the code but was hoping you understood what the number meant. (Why not 96 and 122 or 0 and 26?) In fact 'a' would normally be better than 97, but for this assignment it doesn't matter.