FILE *in_file = fopen("name_of_file", "r"); // read only
FILE *out_file = fopen("name_of_file", "w"); // write only
// test for files not existing.
if (in_file == NULL || out_file == NULL)
{
printf("Error! Could not open file
");
exit(-1); // must include stdlib.h
}
// write to file vs write to screen
fprintf(file, "this is a test %d
", integer); // write to file
fprintf(stdout, "this is a test %d
", integer); // write to screen
printf( "this is a test %d
", integer); // write to screen
// read from file/keyboard. remember the ampersands!
fscanf(file, "%d %d", &int_var_1, &int_var_2);
fscanf(stdin, "%d %d", &int_var_1, &int_var_2);
scanf( "%d %d", &int_var_1, &int_var_2);