Dynamic Array is only returning first element from program

Question

I'm trying to create a function for school that returns an array where any consonants are doubled (ex. Hello = HHellllo). This is my code

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

bool isConsonant(char c) {
    if ((c >=97 && c <= 122 && c != 'a' && c!= 'e' && c!= 'i' && c!= 'o' && c != 'u') | (c >=65 && c <= 90 && c != 'A' && c!= 'E' && c!= 'I' && c!= 'O' && c != 'U')) {
        return true;
    }
    else
        return false;
}

string doubleCons(string i) {
    int len = (int) i.length();
    int numCons = 0;

    for (int j = 0; j < len; j++) {
        if (isConsonant(i[j]) == true) {
            numCons++;
        }
    }
    int s1count = 0;
    string *s1 = new string[len+numCons];
    for (int j = 0; j < (len); j++) {
        if (isConsonant(i[j]) == true) {
            s1[s1count] = i[j];
            s1[s1count+1] = i[j];
            s1count += 2;
        }
        else {
            s1[s1count] = i[j];
            s1count++;
        }
    }
    return *s1;
}


int main() {

    string s = "Hello";
    s = doubleCons(s);
    cout << s << endl;
}

Main is just a test to see if it works. The problem is, the output for main is just H, nothing else.

I've tried looping through s[i] and i just get H????. I can't figure out why the string isn't HHellllo or anything more than H for that matter. Can anybody identify the problem? I've tried debugging with cout statements and I am condiment that isConsonant works fine, as well as the first for loop (numCons = 3 which is correct for hello).

Cheers and hth. - Alf · Accepted Answer · 2014-11-09 05:25:20Z

Problem: in this code,

string doubleCons(string i) {
    int len = (int) i.length();
    int numCons = 0;

    for (int j = 0; j < len; j++) {
        if (isConsonant(i[j]) == true) {
            numCons++;
        }
    }
    int s1count = 0;
    string *s1 = new string[len+numCons];
    for (int j = 0; j < (len); j++) {
        if (isConsonant(i[j]) == true) {
            s1[s1count] = i[j];
            s1[s1count+1] = i[j];
            s1count += 2;
        }
        else {
            s1[s1count] = i[j];
            s1count++;
        }
    }
    return *s1;
}

the

string *s1 = new string[len+numCons];

allocates an array of strings, instead of creating a longer string.

Instead do something like this:

string s1( len+numCons );

Yes it’s that simple.

In other news:

It's not a good idea to use the name i for anything other than a loop counter, since there's a very strong convention using it for that. And by convention i indicates integer. This stems from old Fortran, which got it from mathematics.
Comparision with true is unnecessary and in general an ungood idea (because some C functions return numbers other than 1 to indicate logical true). Consider “I have a house” versus “it’s true that I have a house” versus “it’s true that it’s true that I have a house”, and so on: these comparisons don’t contribute anything useful to the meaning.
Instead of pre-determining the relevant size and then creating a string of that size, you could simply start with an empty result string and use push_back or just += to add characters to the end.

ravi · Accepted Answer · 2014-11-09 05:13:12Z

2

return *s1;

Compiler would treat this as *(s1+0) i.e only first element.

You should return the pointer.

return s1;

Accordingly change the signature of function to

string* doubleCons(string i) {

edited Nov 9, 2014 at 5:13

answered Nov 9, 2014 at 5:07

ravi

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2 Comments

David G Over a year ago

He'll also have to loop through the array and print.

Cheers and hth. - Alf Over a year ago

You're missing the point of the code. The OP is not trying to return an array of strings (in which case the practical solution would be to use a std::vector). The OP is trying to return a longer string.

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