A for-loop as a while statement?

Hi guys,
i'm having some troubles finishing my programm. My programm delete all files that have the same parameter.

So here i read the files and find a specific string:

Code:

if (datei = fopen(filepfad, "a+"))
    {
        while (fgets(buffer, sizeof(buffer), datei)){
            vtNr = 0;
            index = 0;
            str_leng = my_strlen(buffer);

            //So lange das der Teil String "vtNr" nicht gefunden wird, springt der buffer an die nächste Stelle.
            //Wenn die letzte Stelle der Zeile erreicht wurde springt das Programm in die nächste Zeile.(Dokumentaiton zu fgets lesen) 
            while(!( buffer[index] == 'v' && buffer[index + 1] == 't' && buffer[index + 2] == 'N' && buffer[index + 3] == 'r') && index <= (str_leng - 3) )index++;
            
            if ( index < str_leng - 3 )    {
                while(!(buffer[index] >= '0' && buffer[index] <= '9'))index++;
                while(buffer[index] >= '0'  && buffer[index] <= '9')    {
                    vtNr = vtNr * 10 + chartoint(buffer[index]);
                    index++;
                }
                fclose(datei);
                if ( vtNr > 999999) vtNr_vergleichen(vtNr, filepfad);
            }
        }

In the while loop i check if the string is found, but i want that the user determined which string he is looking for. I thought do to it like something like this:

Code:

while( !( for(i=0 ; i < str_end ; i++) buffer[index + i] == str_looking [i]) ) index++;

str_end is the length of the string written by the user.

Thanks for your time .

You can't put for loops within the condition of a while loop in that manner.

I know that it doesn't work, but need any other idea how i can check if my programm has find the String.

Use strstr - C++ Reference