Writing my own strlen function

[Ant Nonumas]

I am trying to write my own strlen fuction, and call it inside main. I feel so close, but I cannot figure out why I get an invalid conversion from 'char*' to 'char' Here is my code:

  #include <iostream>
using namespace std;

char ch[999];

int StringLength(char ch);

int main ()
{
    cout << "Enter a string, and I will output the number of characters contained therein." << endl;
    cin.getline(ch, 999);
    cout << StringLength(ch);

}

int StringLength(char ch)
{
    for (int i = 0, int c = 0; ch[i] != '\0'; i++, c++)
        return c;

}

My error message is as follows: "error: invalid conversion from 'char*" (I guess this is the right symbol used after char) "to 'char' [-fpermissive]
Any help will be greatly appreciated! Thanks

[JLBorges]

#include <iostream>

int StringLength( const char* cstr ); // pass pointer to const char

int main ()
{
    std::cout << "Enter a string, and I will output the number of characters contained therein.\n" ;

    char ch[999] = {} ; // array of 999 char (initialised to all zeroes)

    std::cin.getline( ch, sizeof(ch) );
    std::cout << std::cin.gcount() << " characters were extracted\n" ;

    const int len =  StringLength(ch) ; // implicit conversion from array to pointer
    std::cout << "string length: " << len << '\n' ;
}

int StringLength( const char* ch )
{
    int length = 0 ;
    if( ch != nullptr ) while( ch[length] != '\0' ) ++length ;
    return length ;
}

[cire]

Giving a variable in one scope a name that matches the name of a variable in another scope does not make those names refer to the same variable.

You StringLength has a single char as it's sole parameter. You cannot feed a function which expects a char a pointer-to-char.

Also, your StringLength is equivalent to:

int StringLength(char)
{
    return 0;
}

Assuming the character fed to it is not '\0'. If it is, you have undefined behavior, because the function returns nothing despite it's promise to always return something.

[Ant Nonumas]

As I can see, I will need to read a little further into my book tomorrow morning. I haven't been over pointers and have never seen an example of the "const char*"
Here is what my code looks like after updating it as much as I can tonight. as I really need to get to bed.

#include <iostream>
using namespace std;

char ch[999];

int StringLength(const char* ch);

int main ()
{
    cout << "Enter a string, and I will output the number of characters contained therein." << endl;
    cin.getline(ch, 999);
    cout << StringLength(ch);

}

int StringLength(const char* ch)
{
    for (int i = 0, c = 0; ch[i] != '\0'; i++, c++)
        if (ch[i] == '\0')
            return c;

}

I'm getting a garbage return value, so I am assuming that there is something wrong with my for loop and it never adds to the counter c. I will continue working on this problem in the morning, as I am too tired to continue tonight. Any pointers would be nice, but I will also read more on the s subject

[cire]

The condition governing your for loop is ch[i] != '\0'. So, the for loop does not execute when ch is '\0', meaning that the condition on line 19 will never be true, which means that your function never returns anything.

[Ant Nonumas]

I just jumped back onto the program to see if I could think more clearly now that I've had some rest, and came up with this ( I haven't finished reading the chapter yet like I should.)

    if (ch[i] != '\0')
        for (;ch[i] != '\0'; i++, c++)
        if (ch[i] == '\0') break;
    return c;

Can anyone tell me if there is a more efficient test here? This seems to work though. It counts white spaces, and I am unsure if that is desirable or not. Thanks everyone for the help so far

[cire]

There is no need for both c and i and no need to check for the empty string as an edge case.

std::size_t mystrlen(const char* ch)
{
    std::size_t len = 0;
    while (ch[len])
        ++len;
    return len;
}