Post-class 02/12

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 fflush
 fseek
 ```
+
+---
+
+# Traversing Loops
+
+- Arrays  -> `for`...
+- Strings -> `while(*p != '\0')`
+- Lists   -> `while(p != NULL)`
+- FILES   -> `while(fscanf == x)`
+
+---
+
+[-> Notes 02/12](02-12.md)
diff --git a/02-12.md b/02-12.md
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+[\<- Notes 02/10](02-10.md)
+
+---
+
+# Files Continued
+
+- 2 Ways: Text or Binary
+
+- Regardless, always open the file with `fopen`:
+
+```
+char filename[] = "myFile.txt";
+FILE *fp = fopen(filename, "r");
+```
+
+- The above example opens the myFile.txt for reading
+- The fopen() function takes in two arguments
+	1. the filename
+	2. the mode
+		- "r" -> read
+		- "w" -> write
+		- "a" -> append
+		- "rb" -> read binary
+		- "wb" -> write binary
+		- "ab" -> append binary
+
+- To read a text file:
+
+```
+fscanf(fp, "%d", &x);
+```
+
+- The above example reads the file pointed to by fp for a single integer and stores it in x
+- The fscanf() function takes in three arguments
+	1. the pointer to the file to read
+	2. the data type to read for
+	3. the memory address of the variable to save what was read
+
+- To write to a text file:
+
+```
+fprintf(fp, "%d", x);
+```
+
+- The above example writes the integer x to fp
+- The fprintf() function takes in two arguments
+	1. the pointer to the file to write to
+	2. the text to write
+
+- To read a binary file:
+
+```
+fread(&x, sizeof(int), 1, fp);
+```
+
+- The above example reads 1 int, stores it in variable x from the file pointed to by fp
+- The fread() function takes in four arguments
+	1. variable address to store what is read
+	2. the amount of memory to read
+	3. How many times to read the amount of memory specified in the 2nd argument
+	4. the file pointer to read from
+
+- To write to a binary file
+
+```
+fwrite(x, sizeof(type), 1, fp);
+```
+
+- The above example writes x to the file pointed to by fp
+- The fwrite() function takes in four arguments
+	1. The variable to write from
+	2. the amount of memory being written
+	3. How many times to write the amount of memory specified in the 2nd argument
+	4. the file pointer to write to
+
+- Example: Return the number of integers in a text file greater than 100
+
+```
+int count(FILE *fp){
+	int number, counter = 0;
+	
+	while(fscanf(fp, "%d", &number) == 1){
+		if(number > 100) counter++;
+	}
+
+	return counter;
+}
+```
+
+- Example: Return the average of all the numbers in a text file
+
+```
+int avg(FILE *fp){
+	int number;
+	int sum = 0;
+	int counter = 0;
+
+	while(fscanf(fp, "%d", &number) == 1){
+		sum += number;
+		counter++;
+	}
+
+	return sum/counter;
+}
+```
+
+- Example: Copy a binary file to another file (100 bytes at a time)
+
+```
+FILE *source;
+FILE *dest;
+char srcname[] = "my_source"; //the name of my file
+
+source = fopen(srcname, "rb");
+dest = fopen(srcname, "wb");
+if(source == NULL || dest == NULL) return; //there was an error
+
+void copy_bin(FILE *src, FILE *dest){
+	int r;
+	char x[100]; //store bytes for transfer
+
+	while((r = fread(x, sizeof(char), 100, src)) > 0){
+		fwrite(x, sizeof(char), r, dest);
+	}
+
+return;
+```
+
+- In that last example `r` is used instead of 100 in case there is less than 100 bytes left to read in the file
+- Don't forget to `fclose` at the end!
+
+- Example: Write a function to compare two files, line by line
+
+```
+void compare(FILE *fp1, FILE *fp2){
+	char *r1; //points to x1
+	char *r2; //points to x2
+	char x1[100]; //store from fp1
+	char x2[100]; //store from fp2
+	int line = 1; //what line number I'm looking at
+
+	while(1){
+		r1 = fgets(x1, 100, fp1);
+		r2 = fgets(x2, 100, fp2);
+		if(strcmp(r1, r2) != 0){ //not equal
+			printf("FILES ARE DIFFERENT on line %d\n", line);
+			break;
+		}
+		line++;
+	}
+
+	if(r1 == NULL and r2 == NULL) printf("FILES ARE EQUAL\n");
+
+	return;
+}
+```