This refers to I/O operations from the console (keyboard and screen), which are represented by stdin and stdout.
printf ("print formatted") is used to print data to the screen. It uses format specifiers (like %d) to indicate how to print a variable.
%d or %i: Integer%f: Float%c: Character%s: String (char array)%p: Pointer (address)printf is a variable length argument function, meaning it can take a different number of arguments each time it's called. This is made possible by the ... (ellipsis) syntax, handled by the
scanf ("scan formatted") is used to read data from the keyboard. It uses the same format specifiers as printf.
&) of the variable you want to fill.
int age;
scanf("%d", &age); // Correct
scanf("%d", age); // WRONG: Will crash& because the array name *is* an address.
char name[50];
scanf("%s", name); // CorrectFile handling allows your program to read from and write to files on the disk, making data persistent. All file operations use a special pointer: FILE *fp;.
You must open a file before you can use it. fopen() returns a FILE pointer, or NULL if it fails.
FILE *fp = NULL;
// Open "data.txt" for writing ("w")
fp = fopen("data.txt", "w");
if (fp == NULL) {
printf("Error opening file!\n");
return 1; // Exit
}
// ... do file operations ...
// Always close the file when done
fclose(fp);
Common File Modes:
"r": Read (file must exist)"w": Write (creates file; truncates/overwrites if it exists)"a": Append (creates file; adds to the end if it exists)"rb", "wb", "ab": Same, but for binary files.fscanf() and fprintf(). These are just like scanf/printf, but the first argument is the FILE pointer.
fprintf(fp, "Name: %s, Age: %d\n", "Ravi", 25); int age; fscanf(fp, "%d", &age);
fread() and fwrite(). These read/write raw bytes of data (like a struct) directly. They are much faster and more precise.
struct Student s1; // Write the s1 object to the file fwrite(&s1, sizeof(struct Student), 1, fp); // Read one Student object into s2 struct Student s2; fread(&s2, sizeof(struct Student), 1, fp);
fseek(fp, offset, whence): Moves the file pointer to a specific location.ftell(fp): Returns the current position of the file pointer.rewind(fp): Moves the file pointer back to the beginning of the file.This involves operations that are closer to the hardware, often manipulating individual bits.
This is a repeat from Unit 2. The register keyword suggests to the compiler that a variable should be stored in a CPU register for faster access. It's often used for loop counters, but modern compilers are smart enough to do this automatically.
These operators work on the binary (bit) representation of integers.
| Operator | Name | Example (a=5, b=3) | Result |
|---|---|---|---|
& |
Bitwise AND | 0101 & 0011 |
0001 (1) |
| |
Bitwise OR | 0101 | 0011 |
0111 (7) |
^ |
Bitwise XOR | 0101 ^ 0011 |
0110 (6) |
~ |
Bitwise NOT | ~0101 |
1010 (-6) |
<< |
Left Shift | 0101 << 1 |
1010 (10) |
>> |
Right Shift | 0101 >> 1 |
0010 (2) |
Bit fields allow you to define structure members that are only a specific number of bits wide. This is used to pack data tightly, often for hardware programming.
// This structure packs a date into 16 bits (2 bytes)
struct Date {
unsigned int day : 5; // 5 bits (can hold 0-31)
unsigned int month : 4; // 4 bits (can hold 0-15)
unsigned int year : 7; // 7 bits (can hold 0-127)
};
An enumeration is a user-defined type that consists of a set of named integer constants. It makes code more readable.
// Define an enum for days of the week
enum Weekday { MON, TUE, WED, THU, FRI, SAT, SUN };
int main() {
// By default, MON=0, TUE=1, WED=2, ...
enum Weekday today = WED;
if (today == 2) { // Works, but less readable
//...
}
if (today == WED) { // Much better
//...
}
return 0;
}
This unit re-lists several topics from previous units, likely for reinforcement.
See Unit 3 notes. This refers to int main(int argc, char *argv[]) for receiving arguments when the program is executed.
printf, strcpy, fopen) available in C's standard library. #include and #define.