如何找到数组中第k个字符出现的位置？

Question

I'm writing a program which takes a string, a single character and an integer number k , then it finds the k-th occurence of given character in given string.

I think the code is correct but the code below doesn't give proper results.

char ch[100];
char character;
int n;
cout << endl << "Type a string of characters : ";
gets_s(ch);
cout << endl << "Enter a single Character : ";
cin >> character;
cout << "Enter the event : ";
cin >> n;
if ( func_1( ch,  character,  n)!=-1)
    cout << endl << n << "th event is in the position number  " << (ch, character, n)<< endl;
else
    cout << "Event couldn't be found  ." << endl;
}

 int func_1(char ch[], char character, int n)
 {
    int i = 0;
    int c = 0;

    do
    {
       i++;
    } while (ch[i] != '\0');

    int j;

    for (j = 0; j < i-1;)
    {

        if (ch[j] == character)
            c = c + 1;

        j++;
    }

    if (c == n)
        return j-1;

    else
        return -1;
}

Answer 1

There are a couple of mistakes in func() :

Look at:

do {
    i++;
} while (ch[i] != '\0');   // ouch will loop forever if ch[] is "" !! 

Either use a normal while, or write i=strlen(ch);

Then, when you write this you count all the occurences:

for (j = 0; j < i - 1;) {   // loop unil end of string  
    if (ch[j] == character)
        c = c + 1;            // But if there are several occurences, he will count them all 
    j++;
}

For example, if there are two 'e' in ch[] and you look for the first occurence, when the loop is over, there will be 2 in c, so it will fail !

Rewrite this loop:

for (j = 0; j < i - 1 && c!=n;j++) {   // loop unil end of string => put j++ here for clarity, and exit if you've fount what you've searched
    if (ch[j] == character)
        c++;             
}

But there is also a display issue in you main programme. Look at:

if (func_1(ch, character, n) != -1)
    cout << endl << n << "th event is in the position number  " << (ch, character, n) << endl;

Ok he'll print that he found something, but he will always print n, because (ch, character, n) is not a function call but the comma operator which returns the most right element.

Rewrite this as:

int result = func_1(ch, character, n);
if (result != -1)
    cout << endl << n << "th event is in the position number  " << result << endl;

Answer 2

Well, you have many problems inside the code, but the most relevant part is this one:

for (j = 0; j < i-1;)
{

    if (ch[j] == character)
        c = c + 1;

    j++;
}

if (c == n)
    return j-1;
else
    return -1;

You count the number of occurrences in the whole string, and then check if you were lucky enough to have the exact number of occurrences needed inside the whole string.

What you actually want to do, is to check if you found n-th occurrence inside the loop, like this:

for (j = 0; j < i-1;)
{

    if (ch[j] == character)
        c = c + 1;
    if (c == n)
        return j;  
    j++;
}

Then you probably want to read up on strlen , strchr , and fix other bugs in your code.