"When a file is opened, the file pointer returned by fopen() initially points to the beginning of the file. As you read from it or write to it, the pointer advances through the file content.\n\nTo process a plaintext file we use two functions, fprintf() for output and fscanf() for input. These two functions should look familiar. They work almost exactly the same as printf() and scanf() that work with the standard output and standard input respectively. In fact, the standard in/out are both files so it makes sense that they can be read from/written to. The f prefixed versions are simply generalizations that can be used for any file. The only difference is that the first argument for these two functions is the file you want to output to or read from.\n\nint x = 10;\n\ndouble y = 3.14;\n\n//write to a plaintext file\n\nfprintf(output, \"Hello World!\n\n\");\n\nfprintf(output, \"x = %d, y = %f\n\n\", x, y);\n\n//read from a plaintext file\n\nfscanf(input, \"%d\", &x);\n\nfscanf(input, \"%lf\", &y);\n\n//these are equivalent to printf, scanf:\n\nfprintf(stdout, \"Please enter an integer:\");\n\nfscanf(stdin, \"%d\", &x);"