Counting instances of a character in select lines

Currently learning c++ and I'm pretty stumped. I want to count the instances of a character in a text file - but not including lines that start with a certain character. Specifically, I'm counting instances of Gs and Cs in a text file, but not including lines that begin with "*"

Example<br/>
*metadata information<br/>
atgctaatgcaggtcagtcagtcagtcatgcg<br/>
atgcagtcagtcactgactgactgactgaata<br/>
*metadata information<br/>
atgtagcagctagtcagtcagtcagcatatat<br/>
gatcgactagctgactgacgtactgactgaat<br/>

char Z;
long GC=0;
string Line;
while(getline(InFile, Line)) 
{
    if(Line[0]=='*')
    {
        InFile.get(Z);
        while(InFile.get(Z))
	    {
            if(Z=='G' || Z=='C' || Z=='g' || Z=='c')
            {
                ++GC;
            } 
        } 
    }
}

I'm able to count the instances of g and c across the entire text, but just haven't been able to limit the function to lines that do not begin in >

My understanding of your requirements, you want to ignore lines starting with '*'.

while (getline(InFile, Line))
{
    if (Line[0] == '*')
    {
        continue; // ignore the line
    }
    for (int i = 0; i < Line.length(); ++i)
    {
        const char c = std::toupper(Line[i]);
        if ((c == 'G') || (c == 'C`))
        {
            ++GC;
        }
    }
}

In the above code, if the first line character is '*', the line is ignored.
Otherwise, the string is searched for 'G' or 'C' characters.

    InFile.get(Z);
    while(InFile.get(Z))

You don't want those lines. At this point in your code, the whole string has already been read in string Line;

You probably want

 for(auto c: Line) // go over every char in Line
 {

And you probably want to fix:

if(Line[0] != '*')

because

>but not including lines that start with a certain character.