C Language

char a = 'C';      // single character    %c ''
char b[] = "Trude" // array of characters %s ""
unsigned int // Unsigned. The number must be positive.
int          // Signed. Negative and positive numbers.
char f = 100;                 // %d (number) %c (character)
unsigned char g = 255;        // %d (number) %c (character)
short h = 32767;              // %d
unsigned short i = 65535;     // %d
int j = 2147483647;           // %d
unsigned int k = 4294967295;  // %u
long long l = ...             // %lld
unsigned long long m = ...32U // %llu
float c = 3.141592;           // %f
double d = 3.141592653589793; // %lf

float item1 = 5.75;
printf("Item1: %-8.2\n", item1);

int x = 255;  // Decimal
int y = 0xff; // Hexadecimal

int x = 1, y = 10;
float z = (float) x / (float) y;

const float PI 3.14159;

#define MAX 9

// +  (addition)
// -  (subtraction)
// *  (multiplication)
// /  (division)
// %  (modulus / remainder)
// ++ (increment)
// -- (decrement)
int x = 1;
int y = 2;
int z = x + y; // 3
// Augmented assignment operators
x++; // x = x + 1
y--; // y = y - 1
x+=2; // x = x + 2
x*=2; // x = x * 2

if(a == 1) printf("A is 1.\\n");

if(age == 18){
	printf("You are 18.");
}
else if(age < 0){
	printf("You haven't been born yet.");
}
else{
	printf("You are not 18.");
}

switch(grade){
	case 'A':
		printf("perfect.\n");
		break;
	case 'B':
		printf("good.\n");
		break;
	case 'C':
		printf("okay.\n");
		break;
	case 'D':
		printf("meh.\n");
		break;
	case 'F':
		printf("failed.\n");
		break;
	default:
		printf("Enter only valied grades.\n");
}
// If break; is missing, the next case is also executed.

if(temp >= 0 && temp <= 30){
	printf("\nThe weather is good.")
}

if(temp <= 0 || temp >= 30){
	printf("\nThe weather is good.")
}

if(!(temp <= 0 || temp >= 30)){
	printf("\nThe weather is bad.")
}

// (condition) ? value if true : value if false
int max = (x > y) ? x : y;

int x = 6;  // 6  = 00000110
int y = 12; // 12 = 00001100
int z = 0;  // 0  = 00000000
z = x & y;  // AND         - 00000100 (4)
z = x | y;  // OR          - 00001110 (14)
z = x ^ y;  // XOR         - 00001010 (10)
z = x << 1; // Left Shift  - 00001100 (12) (Shift all bits to the left.)
z = x >> 1; // Right Shift - 00000011 (3)  (Shift all bits to the right.)

void myFunction(); // Function Prototype
int main() {
	myFunction(); // Call function
	return 0;
}
void myFunction() { // Function Definition
	//...
}

void greet(char x[], int y);
int main() {
	char name[] = "Trude";
	int age = 132;
	greet(name, age);
}
void greet(char x[], int y) {
	printf("\nHello %s, you are %d years old.", x, y);
}

double square(double x);
int main() {
	double x = square(3.14);
	printf("%lf", x);
	return 0;
}
double square(double x) {
	return x * x;
}

int i = 0;
void plusOne(int n) {
	printf("%d", n);
	if (n < 10000) plusOne(n);
}

void hello(char[], int); // Function Prototype
int main() {
	hello(//...);
	return 0;
}
void hello(char name[], int age){
	//...
}

for(int i = 0; i < 10; i++){
	printf("%d\n", I); //0-9
}
//Multiple initial variables
for(int i = 0, int y = 1; i < 10; i++){
	printf("%d\n", I); //0-9
}

while(test == 1){
	printf("Test is not 1.\n");
}

do {
	printf("Enter a number above 0: ");
	scanf("%d", &number)
} while (number > 0);

while (true) {
	...
}

struct Player {
	char name[12];
	int score;
};
int main(){
	struct Player player1;
	struct Player player2;
	strcpy(player1.name, "Trude");
	player1.score = 4;
	strcpy(player2.name, "JCionx");
	player2.score = 7;
	player1.score; //4
}

struct Student {
	char name[12];
	float gpa;
};
int main() {
	struct Student s1 = {"Peter", 3.0};
	struct Student s2 = {"Jean", 4.0};
	struct Student s3 = {"David", 2.5};
	struct Student students[] = {s1, s2, s3};
	printf("%f\n", students[0].gpa); // Print the student 1 gpa.
	return 0;
}

typedef char user[25];
int main() {
	user user1 = "Trude";
}

typedef struct {
	char name[25];
	char password[12];
	int id;
} User;
int main(){
	User user1 = {"Trude", "hello123", 12335};
}

\0 // This character represents 00000000 and marks the end of a string.
// Same as 0x0 and null.

int main(int argc, char argv[]) {
	if (argc == 2) {
		printf("hello, %s\n", argv[1]);
	} else {
		printf("You need to add 1 argument.\n");
		return 1;
	}
	return 0;
}

// enum Day{Sun, Mon, Tue, Wed, Thu, Fri, Sat}; (This enum starts from 0 to 6.)
enum Day{Sun = 1, Mon = 2, Tue = 3, Wed = 4, Thu = 5, Fri = 6, Sat = 7};
int main(){
	enum Day today = Sun;
	if(today == Sun || today == Sat){
		printf("It's the weekend.");
	}
}

int age = 21;
int *pAge = &age;
int valueOfAge = *pAge;
printf("%p and %p are the same.", &age, pAge);

/* Use char[] when:
		- The maximum string length is known.
		- No need to modify the whole string.
		- No need to pass the string to a function [that modifies it]
*/
char name[] = "Trude"; // 6 bits on stack memory.
name[0] = 'T'; // Elements of an array can be modified.
/* Use char* when:
		- The maximum string length is NOT known.
		- The string will later be modified.
		- The string will be passed to a function [that modifies it].
*/
const char *name = "Trude"; // 8 bits in stack + 6 bits read-only.
name = "TrudeEH"; // Pointers can be overwritten.
name++; // rudeEH - Works because the pointer is shifted to the next value.
peintf("%c\n", *(name+1)); // Prints 'r'.
printf("%c\n", name[1]); // Works with both for reading.
printf("%s\n", name);    // Print a string.
// The string in memory:
// [T][r][u][d][e][\\0]
// The memory address of T is stored.

#include <stdio.h>
#include <string.h>
char s* = "Trude";
char t* = "Trude";
if (strcmp(s, t) == 0) {
	printf("Same string.");
}

#include <stdlib.h>
char *s = "Trude";
char *t = malloc(strlen(s) + 1);
// 2 variables are declared, so strlen isn't called with every iteration.
for (int i = 0, n = strlen(s) + 1; i < n; i++) {
	t[i] = s[i];
)
//...
free(t);

#include <stdlib.h>
#include <string.h>
char *s = "Trude";
char *t = malloc(strlen(s) + 1);
strcpy(t, s);
//...
free(t);

#include <stdio.h>
int main(void){
	int x;
	scanf("%i", &x);
}

#include <stdio.h>
int main(void){
	char s[4];
	scanf("%4s", s);  //No &, s is an address already.
}

#include <stdio.h>
#include <string.h>
int age;
char name[25];
printf("What is your name? ");
fgets(name, 25, stdin); // name of variable, max size, input.
name[strlen(name)-1] = '\0'; // removes the line break fgets adds. String library is required.
printf("How old are you? ");
scanf("%d", &age);

#include <stdio.h>
int main() {
	FILE *file = fopen("test.txt", "w"); // w - overwrite / a - append
	fprintf(file, "Some Text");
	fclose(file);
	return 0;
}

#include <stdio.h>
int main() {
	if(remove("test.txt") == 0){
		printf("File removed.\n");
	} else {
		printf("Failed to delete file.\n");
	}
	return 0;
}

#include <stdio.h>
int main() {
	FILE *pF = fopen("test.txt", "r") // r - read.
	char buffer[255]; // Will hold 1 line of the file.
	if(pF == NULL){
		printf("File does not exist.");
		return 1;
	}
	fgets(buffer, 255, pF);
	printf("%s", buffer); // Print first line of file. Use in a while loop to print all of them.
	fclose(pF);
	return 0;
}