fwrite in C giving different values in output files

Question

why are the output files different when I use fwrite in another function VERSUS fwrite in the same function?

output1.txt contains garbage value like Ê, which is NOT corr

Answer 1

In function writeData change

fwrite(&buf, sizeof(char), strlen(buf), fp1);

to

fwrite(buf, sizeof(char), strlen(buf), fp1);