Practice Programs

1.

#include <stdio.h>
 
int main() {
	char hello[] = "Hello!"; // Strings in C is a char[] that ends in null (ASCII 0)
	char hello2[] = {72, 101, 108, 111, 33, 0}; // uses ASCII to represent the individual characters
	
	puts(hello); // puts() --> print new line function
	puts(hello2);
}

gcc hello.c -o hello # compiles the c program source code
./hello # Run the program
Hello!
Hello!

gcc hello.c -o hello

• gcc: the compiler name
• hello.c: the file in c
• -o hello: name the output file hello instead of a.out

WARNING

-o is dependent of the program’s integration. Generally stands for a flag for Output

Note

In memory:

• hello1: represented H in an 8 bit but specified in characters, etc.
• hello2: represented H in an 8 bit but specified in integers, etc.

2.

#include <stdio.h>
 
int main() {
	char hello[] = "Hello!";
	char hellonum[] = {72, 101, 108, 108, 111, 33, 0};
	char hellobin[] = {0b1001000, 0b1100101, 0b1101100, 0b1101100, 0b1101111, 0b100001, 0b0};
	
	puts(hello);
	puts(hellonum);
	puts(hellobin);
	
	printf("%c %c %c\n", hello[0], hello[1], hello[2]);
	printf("%d %d %d\n", hello[0], hellonum[0], hellobin[0]);
	printf("%c %c %c\n", hello[0], hellonum[0], hellobin[0]);
}

gcc hellobin.c -o hellobin
./hellobin
 
Hello!
Hello!
Hello!
H e l
72 72 72
H H H

Flow of keyboard keys

Press A → Closed the circuit and send a electrical signal → Keyboard controller

• Moving the letters through the buffer → Buffer where the last n keys pressed
• n boxes to store the last n characters pressed
• Each box (on a full US-keyboard layout)→ about 100 little bit boxes (0/1) → ~100 bits per character (not optimal) → Can we do better?
  • Use ASCII → uses 7 bits instead of 100 bits
  • With 7 bits we can represent $2^7$ or $128$ different characters, which is sufficient to store most if not all characters in the US layout

NOTE

Why not 8 bits? With 8 bits, the amount of unique characters that the system can represent is 256

→ Flip-Flop Gate

• 0 and 1 signal input
• A physical gate sticks to either 0 or 1
• SRAM → Static Random Access Memory
  • Volatile Memory: Loses the data stored when power off
  • Cheap silicon (Sand)
  • Fast (100m/times/sec)
  • Accurate (as long as the power is on)