exmaple.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <time.h>

#define FLAG_BUFFER 128
#define MAX_SYM_LEN 4

typedef struct Stonks {
	int shares;
	char symbol[MAX_SYM_LEN + 1];
	struct Stonks *next;
} Stonk;

typedef struct Portfolios {
	int money;
	Stonk *head;
} Portfolio;

int view_portfolio(Portfolio *p) {
	if (!p) {
		return 1;
	}
	printf("\nPortfolio as of ");
	fflush(stdout);
	system("date"); // TODO: implement this in C
	fflush(stdout);

	printf("\n\n");
	Stonk *head = p->head;
	if (!head) {
		printf("You don't own any stonks!\n");
	}
	while (head) {
		printf("%d shares of %s\n", head->shares, head->symbol);
		head = head->next;
	}
	return 0;
}

Stonk *pick_symbol_with_AI(int shares) {
	if (shares < 1) {
		return NULL;
	}
	Stonk *stonk = malloc(sizeof(Stonk));
	stonk->shares = shares;

	int AI_symbol_len = (rand() % MAX_SYM_LEN) + 1;
	for (int i = 0; i <= MAX_SYM_LEN; i++) {
		if (i < AI_symbol_len) {
			stonk->symbol[i] = 'A' + (rand() % 26);
		} else {
			stonk->symbol[i] = '\0';
		}
	}

	stonk->next = NULL;

	return stonk;
}

int buy_stonks(Portfolio *p) {
	if (!p) {
		return 1;
	}
	char api_buf[FLAG_BUFFER];
	FILE *f = fopen("api","r");
	if (!f) {
		printf("Flag file not found. Contact an admin.\n");
		exit(1);
	}
	fgets(api_buf, FLAG_BUFFER, f);

	int money = p->money;
	int shares = 0;
	Stonk *temp = NULL;
	printf("Using patented AI algorithms to buy stonks\n");
	while (money > 0) {
		shares = (rand() % money) + 1;
		temp = pick_symbol_with_AI(shares);
		temp->next = p->head;
		p->head = temp;
		money -= shares;
	}
	printf("Stonks chosen\n");

	// TODO: Figure out how to read token from file, for now just ask

	char *user_buf = malloc(300 + 1);
	printf("What is your API token?\n");
	scanf("%300s", user_buf);
	printf("Buying stonks with token:\n");
	printf(user_buf);

	// TODO: Actually use key to interact with API

	view_portfolio(p);

	return 0;
}

Portfolio *initialize_portfolio() {
	Portfolio *p = malloc(sizeof(Portfolio));
	p->money = (rand() % 2018) + 1;
	p->head = NULL;
	return p;
}

void free_portfolio(Portfolio *p) {
	Stonk *current = p->head;
	Stonk *next = NULL;
	while (current) {
		next = current->next;
		free(current);
		current = next;
	}
	free(p);
}

int main(int argc, char *argv[])
{
	setbuf(stdout, NULL);
	srand(time(NULL));
	Portfolio *p = initialize_portfolio();
	if (!p) {
		printf("Memory failure\n");
		exit(1);
	}

	int resp = 0;

	printf("Welcome back to the trading app!\n\n");
	printf("What would you like to do?\n");
	printf("1) Buy some stonks!\n");
	printf("2) View my portfolio\n");
	scanf("%d", &resp);

	if (resp == 1) {
		buy_stonks(p);
	} else if (resp == 2) {
		view_portfolio(p);
	}

	free_portfolio(p);
	printf("Goodbye!\n");

	exit(0);
}

ubsubscription.c

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <ctype.h>

#define FLAG_BUFFER 200
#define LINE_BUFFER_SIZE 20


typedef struct {
	uintptr_t (*whatToDo)();
	char *username;
} cmd;

char choice;
cmd *user;

void hahaexploitgobrrr(){
 	char buf[FLAG_BUFFER];
 	FILE *f = fopen("flag.txt","r");
 	fgets(buf,FLAG_BUFFER,f);
 	fprintf(stdout,"%s\n",buf);
 	fflush(stdout);
}

char * getsline(void) {
	getchar();
	char * line = malloc(100), * linep = line;
	size_t lenmax = 100, len = lenmax;
	int c;
	if(line == NULL)
		return NULL;
	for(;;) {
		c = fgetc(stdin);
		if(c == EOF)
			break;
		if(--len == 0) {
			len = lenmax;
			char * linen = realloc(linep, lenmax *= 2);

			if(linen == NULL) {
				free(linep);
				return NULL;
			}
			line = linen + (line - linep);
			linep = linen;
		}

		if((*line++ = c) == '\n')
			break;
	}
	*line = '\0';
	return linep;
}

void doProcess(cmd* obj) {
	(*obj->whatToDo)();
}

void s(){
 	printf("OOP! Memory leak...%p\n",hahaexploitgobrrr);
 	puts("Thanks for subsribing! I really recommend becoming a premium member!");
}

void p(){
  	puts("Membership pending... (There's also a super-subscription you can also get for twice the price!)");
}

void m(){
	puts("Account created.");
}

void leaveMessage(){
	puts("I only read premium member messages but you can ");
	puts("try anyways:");
	char* msg = (char*)malloc(8);
	read(0, msg, 8);
}

void i(){
	char response;
  	puts("You're leaving already(Y/N)?");
	scanf(" %c", &response);
	if(toupper(response)=='Y'){
		puts("Bye!");
		free(user);
	}else{
		puts("Ok. Get premium membership please!");
	}
}

void printMenu(){
 	puts("Welcome to my stream! ^W^");
 	puts("==========================");
 	puts("(S)ubscribe to my channel");
 	puts("(I)nquire about account deletion");
 	puts("(M)ake an Twixer account");
 	puts("(P)ay for premium membership");
	puts("(l)eave a message(with or without logging in)");
	puts("(e)xit");
}

void processInput(){
  scanf(" %c", &choice);
  choice = toupper(choice);
  switch(choice){
	case 'S':
	if(user){
 		user->whatToDo = (void*)s;
	}else{
		puts("Not logged in!");
	}
	break;
	case 'P':
	user->whatToDo = (void*)p;
	break;
	case 'I':
 	user->whatToDo = (void*)i;
	break;
	case 'M':
 	user->whatToDo = (void*)m;
	puts("===========================");
	puts("Registration: Welcome to Twixer!");
	puts("Enter your username: ");
	user->username = getsline();
	break;
   case 'L':
	leaveMessage();
	break;
	case 'E':
	exit(0);
	default:
	puts("Invalid option!");
	exit(1);
	  break;
  }
}

int main(){
	setbuf(stdout, NULL);
	user = (cmd *)malloc(sizeof(user));
	while(1){
		printMenu();
		processInput();
		//if(user){
			doProcess(user);
		//}
	}
	return 0;
}