Finding the index of a char in an array with a pointer as an argument

Question

I have a main function which has the code:

int main()
{
    const int SIZE = 80;
    char ca[SIZE];
    char * pc = ca;
    int fPrints = 0;
    int bPrints = 0;
    int lengthChecks = 0;

    ReadString(pc, SIZE);
    char test = 'X';
    int index = 0;
    index = FindIndexOfCharacter(pc, test);
    std::cout << test << " index " << index << std::endl;
    test = 's';
    index = 0;
    index = FindIndexOfCharacter(pc, test);
    std::cout << test << " index " << index << std::endl;

    std::cout << "Press ENTER";
    std::cin.get();
    return 0;
}

A function which reads the input

void ReadString(char * c, int maxLength)
{
    std::cout << "Enter a string less than " << maxLength << " characters." << std::endl;

    std::cin.getline(c, maxLength);
}

This function is supposed to return the index of a character in the array by using the pointer to the array and a test value and return it

int FindIndexOfCharacter(char * c, char testVal) 
{
    for (int i = 0; i < strlen(c); i++)
    {
        if (c[i] == testVal) {
            return (int)i;
        }
        else
        {
            return -1;
        }
    }

}

All I get is -1 for both searches, I am not sure what I am doing wrong. Would appreciate any help!

"All I get is -1 for both searches." What searches? You didn't show what kind of input you give to get that result. [ot] Why do you cast an int to an int? And you should probably not leave open the possibility that the compiler calls strlen() on every iteration of the loop. More to the point, you should not use int for sizes; that's why std::size_t exists (not that it matters until you start having strings > 2.1billionish characters long, but still...) — underscore_d
– underscore_d, Commented Oct 26, 2017 at 21:28
@underscore_d Would I be better off using a variable length in the function which equals strlen() and then using it in the loop? — Sarah Hyland
– Sarah Hyland, Commented Oct 26, 2017 at 21:30
I'd say so. For example, for (std::size_t i = 0, len = strlen(c); i < len; ++i). Of course, first #include <cstddef> to get the declaration of std::size_t. — underscore_d
– underscore_d, Commented Oct 26, 2017 at 21:31

frslm · Accepted Answer · 2017-10-26 21:30:59Z

3

You're returning too early in FindIndexOfCharacter()! If the very first character you come across doesn't match testVal, FindIndexOfCharacter() will return prematurely.

Try moving return -1; after the for-loop; this way, you'd return -1 only after you've checked every character in c:

int FindIndexOfCharacter(char * c, char testVal) 
{
    for (int i = 0; i < strlen(c); i++)
    {
        if (c[i] == testVal) {
            return (int)i;
        }
    }

    return -1;
}

answered Oct 26, 2017 at 21:30

frslm

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1 Comment

Sarah Hyland Over a year ago

That did it! Appreciate it!

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