Need some help again. The user is inputting some values in the docreate() function and I need these values back in the main function to print them. I have tried but unable to achieve the goal. I just one characteristic of the drone (name) for now for printing when the user enters 2 in the main code. The code is below:
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
struct drone_t{
char name[30];
float top_s;
float acc;
};
struct do_create(int dronesCreated);
#define MAXDRONES 3
int main()
{
struct drone_t drone;
int dronesCreated = 0;
int i;
char namee;
while(1)
{
printf("1. Create Drone\n2. Calculate Time\n3. Exit\n");
scanf("%d", &i);
if (i == 1)
{
if(dronesCreated<=MAXDRONES-1)
{
dronesCreated++;
do_create(dronesCreated);
}
else
{
printf("error: cannot create more drones\n");
}
}
else if (i == 2)
{
printf("%s", drone[dronesCreated].name);
}
else if (i == 3)
{
exit(EXIT_SUCCESS);
}
else
{
printf("error: select an option between 1 and 3\n");
}
}
}
void do_create(int dronesCreated)
{
struct drone_t drone[dronesCreated];
printf("What is the name of the drone?\n");
scanf("%s", drone[dronesCreated].name);
printf("What is the top speed of the drone? (kmph)\n");
scanf("%f", &drone[dronesCreated].top_s);
printf("What is the acceleration of the drone? (mpsps)\n");
scanf("%f", &drone[dronesCreated].acc);
return drone.name;
}
Your code has few errors, fixing them as follow may give you the desired results you are looking for:
struct do_create(int dronesCreated); is an invalid declaration and it should be void do_create(int dronesCreated);
you are using drone variable in main as an array but it was declared as drone_t struct, so it should be declared as an array as following: struct drone_t drone[MAXDRONES];
char namee; is never used and either should be removed or should be used
arrays in C are 0 indexed, but dronesCreated index was initialized to 0 and incremented by 1 in the first if statement, so it will start from 1 instead of 0. Therefore, you have either to initialized it with -1 and when incremented by 1 inside the if statement it then will start from index 0, or you have to incremented it after invoking the do_create
do_create is declared as void but you are trying to return some value (char* in your case), so you may change it to return struct drone_t
inside do_create you redefine struct drone_t drone[dronesCreated] which was defined in main, note that drone variable in do_create will be the drone defined in the clsoest scope, which is the local variable and modifying it will not affect the one defined in main. So, either you have to define it as global variable, to pass it to do_create as a parameter, or to make do_create return new struct drone_t to main and in main to assign it in drone array.
Related
I'm working on the last exercise of the "Think like a computer scientist, C version" book and I have some trouble with one particular point.
The exercise consists of making a small game, where the computer picks a random value between 0 and 20 and then asks me to guess the number.
After that, the computer counts the number of tries I made and, if I get a better score than the previous party, I need to store my name and the number of tries in a structure.
My problem is the following: When I restart the game, the string value, player_name, in the structure gets somehow deleted but player_score is still there.
First, I made a "call by value" function to create the structure and then a tried with a "call by reference" but getting the same results.
I think I tried everything I could with my actual knowledge for now; so, if someone could check my code and give me some tips about what's wrong I would much appreciate it!
//HEADERS
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define FALSE 0
#define TRUE 1
//TYPEDEF STRUCTS
typedef struct
{
int player_score;
char *player_name;
} HS_Player;
//FUNCTION PROTOTYPES
int Random_Value(void);
int Get_User_Choice(void);
int Check_Result(int computer, int my_choice);
int Try_Again(int game_result, int computer);
void Player_Infos(HS_Player *player_p, int score);
int Game_Restart(void);
//MAIN
int main(void)
{
int end_game;
int high_score_value = 100;
HS_Player player;
while (end_game != TRUE)
{
int computer_number = Random_Value();
printf("Guess the number between 0 et 20 chosen by the computer.\n");
int your_number = Get_User_Choice();
int result_game = Check_Result(computer_number, your_number);
int tries_to_win = Try_Again(result_game, computer_number);
printf("Number of tries: %i\n", tries_to_win);
if (tries_to_win < high_score_value)
{
Player_Infos(&player, tries_to_win );
high_score_value = player.player_score;
}
printf("Highest score: %i By: %s\n", player.player_score, player.player_name);
printf("\n");
end_game = Game_Restart();
}
return EXIT_SUCCESS;
}
//Random_Value FUNCTION
int Random_Value(void)
{
srand(time(NULL));
int x = rand();
int y = x % 20;
return y;
}
//Get_User_Choice FUNCTION
int Get_User_Choice(void)
{
int success, x;
char ch;
printf("Your Guess:\t");
success = scanf("%i", &x);
while (success != 1)
{
printf("Your input is not a number. Please try again:\t");
while ((ch = getchar()) != '\n' && ch != EOF);
success = scanf("%i", &x);
}
if (x < 0 || x > 20)
{
printf("Your input must be between 0 and 20. Please try again.\n");
Get_User_Choice();
}
return x;
}
//Check_Result FUNCTION
int Check_Result(int computer, int my_choice)
{
int check_result;
if (my_choice < computer)
{
printf("Computer number is larger!\n");
check_result = FALSE;
}
else if (my_choice > computer)
{
printf("Computer number is smaller!\n");
check_result = FALSE;
}
else if (my_choice == computer)
{
printf("It's a Match! You chose the same number than the computer.\n");
printf("\n");
check_result = TRUE;
}
return check_result;
}
//Try_Again FUNCTION
int Try_Again(int game_result, int computer)
{
int tries_befor_success = 1;
while (game_result != TRUE)
{
int your_number = Get_User_Choice();
game_result = Check_Result(computer, your_number);
tries_befor_success++;
}
return tries_befor_success;
}
//Player_Infos FUNCTION
void Player_Infos(HS_Player *player_p, int score)
{
char new_name[80];
printf("Congrats! Your made a new high score.\n");
printf("What's your name ?\t");
scanf("%s", new_name);
printf("\n");
player_p->player_score = score;
player_p->player_name = new_name;
}
//Game_Restart FUNCTION
int Game_Restart(void)
{
int quit_value;
printf("Quit Game ?\n");
printf("Press 'y' to quit or any other keys to continue.\n");
fflush(stdin);
char quit_game = getchar();
printf("\n");
if (quit_game == 'y')
{
quit_value = TRUE;
}
else
{
quit_value = FALSE;
}
return quit_value;
}
The problem is that, in your Player_Infos function, you are assigning the address of a local array to the char* player_name pointer member of the passed structure. When that function ends, the local array it used will be deleted and the pointer in the structure will be invalid. (In the case of the player_score, you don't have that problem, because the given value is copied to the structure member.)
There are several ways around this; one would be to use the strdup() function to make a copy of the local char new_name[80]; array – but that is really overkill, and you would need to manage (i.e. free()) that allocated string whenever you make a modification.
A simpler way is to make the player_name member an actual array of char and then use strcpy() to copy the local array into that member.
Better, still, with the player_name member defined as char [80], you can read directly into that (in the function), and avoid the local array completely:
typedef struct
{
int player_score;
char player_name[80];
} HS_Player;
//...
void Player_Infos(HS_Player *player_p, int score)
{
printf("Congrats! Your made a new high score.\n");
printf("What's your name ?\t");
// Read directly. Limit input to 79 chars (allowing room for null terminator).
scanf("%79s", player_p->player_name);
printf("\n");
player_p->player_score = score;
}
Also, just as a "style" tip, you may want to change the member names to just score and name, as the "player" part is implied by the structure type-name itself.
This issue you are having is that you are associating the player name pointer to a variable that goes out of scope when you leave the "player_Infos" function. What you probably would want to do is define the name as a character array in your structure and then use the "strcpy" call in your function instead. Following is a couple of code snippets illustrating that point.
//TYPEDEF STRUCTS
typedef struct
{
int player_score;
char player_name[80];
} HS_Player;
Then, in your function, use the "strcpy" call.
//Player_Infos FUNCTION
void Player_Infos(HS_Player *player_p, int score)
{
char new_name[80];
printf("Congrats! Your made a new high score.\n");
printf("What's your name ?\t");
scanf("%s", new_name);
printf("\n");
player_p->player_score = score;
strcpy(player_p->player_name, new_name);
//player_p->player_name = new_name;
}
When I tested that out, I got a name to appear in the terminal output.
Computer number is smaller!
Your Guess: 4
It's a Match! You chose the same number than the computer.
Number of tries: 8
Highest score: 4 By: Craig
FYI, you will need to include the "string.h" file.
Give that a try.
Name Update
The reason your player.player_name is not getting updated is because you can't assign a string this way in C. When doing player_p->player_name = new_name; you're actually saving in player_p->player_name the memory address of new_name.
Instead, what you want to achieve, is to copy each character of new_name to player_p->player_name and in order to achieve this, you have to change the type of prlayer_name field from char* player_name to char player_name[80], then assign it using, for example, strcpy():
#include <string.h>
// [...]
//TYPEDEF STRUCTS
typedef struct
{
unsigned int player_score;
char player_name[80];
} HS_Player;
// [...]
//Player_Infos FUNCTION
void Player_Infos(HS_Player *player_p, int score)
{
char new_name[80];
printf("Congrats! Your made a new high score.\n");
printf("What's your name ?\t");
scanf("%s", new_name);
printf("\n");
player_p->player_score = score;
strcpy(player_p->player_name, new_name);
}
Data Persistence
To make data (players info) persistent over multiple runs, you have to save the content of the struct to a file.
Example
int Save_Score(char* filename, HS_Player* player)
{
FILE* file = fopen(filename, "w");
if (file == NULL)
{
fprintf(stderr, "\nAn error occurred while opening the file\n");
return -1;
}
if (fprintf(file, "%d %s", player->player_score, player->player_name) < 0)
return -1;
fclose(file);
return 0;
}
int Load_Score(char* filename, HS_Player* player)
{
FILE* file = fopen(filename, "r");
if (file == NULL)
{
fprintf(stderr, "\nAn error occurred while opening the file\n");
return -1;
}
if (fscanf(file, "%d %79s", &player->player_score, player->player_name) < 0)
return -1;
fclose(file);
return 0;
}
I want to display structure members based on user input, but I don't know if I've stored the input properly.
When I try display all people, it just outputs random numbers.
These are the structures and function prototypes
#define MAX_NAME_LEN 15
#define MAX_NUM_PERSON 4
#define MAX_JOB_LENGTH 20
typedef struct birth_date
{
int month;
int day;
int year;
} person_birth_t;
typedef struct person
{
char pName[MAX_NAME_LEN];
char job[MAX_JOB_LENGTH];
person_birth_t birth_t;
} person_t[MAX_NUM_PERSON];
void print_menu (void);
void scanPerson(person_t p, int);
void displayPeople(person_t p);
This is the main code for the program, a menu is printed asking user to input a number, if a user enters 1 then it prompts them to add a person. Entering 2 displays all people entered.
int main(void)
{
/* TODO */
print_menu();
return 0;
}
void print_menu (void)
{
int choice;
person_t p;
static int index = 0;
int *indexP = NULL;
indexP = &index;
/*Print the menu*/
scanf("%d", &choice);
switch (choice)
{
case 1:
if (index < MAX_NUM_PERSON){
scanPerson(p, index);
++*indexP;
print_menu();
} else {
printf("Can't add more people - memory full \n");
print_menu();
}
break;
case 2:
displayPeople(p);
break;
case 3:
exit(0);
break;
default:
print_menu();
}
}
/*function called when add person is chosen from menu */
void scanFlight(person_t p, int index){
/*printf to enter name*/
scanf(" %s", p[index].pName);
/*printf to enter job*/
scanf("%s", p[index].job);
}
void displayPeople(person_t p){
for(int i = 0; i < MAX_NUM_PERSON; i++){
printf("%s %d-%d-%d %s \n",p[i].pName
,p[i].birth_t.month
,p[i].birth_t.day
,p[i].birth_t.year
,p[i].job);
}
}
I've tried other ways to take input and add it to a struct array, but I'm just not sure how to do it right.
person_t p;
Here, you use the local variable p (in print_menu function), so each recursion, you just print the parameters of the local variable that is not initialized.
To solve it, you can declare p as the global variable.
OT, in scanFlight function, to avoid overflow, you should change the scanf function to:
/*printf to enter name*/
scanf("%14s", p[index].pName);
/*printf to enter job*/
scanf("%20s", p[index].job);
And, rename scanPerson to scanFlight, because i do not see any implementation of scanPerson function in your code. I think it's typo, no ?
None of the methods were working, so instead of trying to figure it out, I scrapped the static index and indexP.
Instead, I initialized p with malloc:
person_t *p= malloc(MAX_NUM_PERSON * sizeof(person_t));
I changed the scan function to accommodate for the change and made index a pointer instead, and I made the display function pass the index.
When I ran it, the output was correct.
#include <stdio.h>
#include <stdlib.h>
int (*(*ptr[2])[2])(); //arr of pointers to the array of func pointer
int (*arr_1[2])(int ,int);//arr of function pointers
(*arr_1[])()={add1, sub1};//add1 ,sub1 are simple functions returning int
int (*arr_2[2])(int ,int);
int a,b, user_func_choice;
(*arr_2[])()={add2, sub2};
int lib_choice,user_lib_choice;
int main(int argc , char* argv[]) {
printf("enter the lib number\t 1:Lib1 , 2:Lib2 \n");
scanf("%d", &user_lib_choice);
lib_choice=user_lib_choice-1;
if(lib_choice==0){
printf("Welcome to lib1\n");
printf("enter func choice==> 1: Add , 2: subtract\n");
scanf("%d", &user_func_choice);
printf("enter the numbers.\n");
scanf("%d%d",&a,&b);
int func_choice= user_func_choice-1;
ptr[0]= arr_1;
if(func_choice==0)
{
int sum1=(*(*ptr[lib_choice])[func_choice])(a,b);
printf("sum1=%1d\n\n", sum1);
}
else if(func_choice==1)
{
int subtract1=(*(*ptr[lib_choice])[func_choice])(a,b);
printf("sub1=%1d\n\n", subtract1);
}
else{printf("InValid Function/operator choice\n");}
return;
}
if(lib_choice=1){
int a, b, user_func_choice;
printf("welcome to lib2\n");
printf("enter func choice: 1: Add , 2: subtract\n");
scanf("%d", &user_func_choice);
printf("enter the numbers.\n");
scanf("%d%d",&a,&b);
ptr[1] = arr_2;
int func_choice= user_func_choice-1;
if(func_choice==0)
{
int sum2=(*(*ptr[lib_choice])[func_choice])(a,b);
printf("sum2=%1d\n\n", sum2);
}
else if(func_choice==1)
{
int subtract2=(*(*ptr[lib_choice])[func_choice])(a,b);
printf("sub2=%1d\n\n", subtract2);
}
return;
}
else{printf("InValid library choice\n");
}
return 0;
}
Every thing works fine here
But what i want is instead of hardcoding the initialization of library(lib1 or lib2) let user specify the number of libraries he want to intialize. Something like this
int main(int argc , char* argv[]){
printf("enter the lib number\t 1:Lib1 , 2:Lib2 \n");
scanf("%d", &user_lib_choice);
if(argc!=2){printf("please specify the library number as sencond argument\n");return 0;}
int lib_choice_cmd=atoi(argv[1]);
if(lib_choice==1)
{
lib1_init();
}
else if(lib_choice==2)
{
lib1_init();
lib2_init();
}
lib_init() is the function that will do the initialization process.If user specify lib num as 1 i will initialize only lib1. I did this for lib1, but this gives me an error
lib1_init(){
(*arr_1[2])(int ,int)={add1 , sub1};
}
And when i did
lib1_init(){
arr_1[0]=add1;
arr_1[1]=sub1;
}
This gives me a segmentation fault.Pleae tell me what is wrong
You can only do initialization when initializing, not later. Even given that, your syntax looks odd.
You can of course use plain assignment to each element:
void array_init(void)
{
arr_1[0] = add1;
arr_1[1] = sub1;
}
(*arr[2])()={add1 ,sub1};
Unless that line appears on the same line as the function pointer array initialization, it is complete nonsense code.
You can initialize the array upon declaration like this:
int(*arr[2])(int ,int) = {add1 ,sub1};
Or you can assign an individual item, just as for any array:
arr[0] = add1;
In C, you cannot assign arrays to arrays, nor can you assign several array items on a single line. That is, you can't do int arr[2]; arr = {1,2};Function pointer arrays are no different than other arrays.
If you want to initialize the array in run-time, you have to either set each item one by one in a loop, or use memcpy.
I did not right understood the problem, but there is a syntax mistake:
if you declare a pointer to function array like this:
int(*arr[2])(int ,int)
you have to call the function like this:
(*arr[0])(some_int_stuff, some_other_int_stuff);
the mistakes are that the index must be smaller than 2, and you don't pass any parameter
I am currently trying to store information that is input from a function to a struct declared in my header file and utilize it within the main file. I cannot use struct arrays because I am not allowed to allocate memory.
header file
#ifndef HOMEWORK_H_
#define HOMEWORK_H_
typedef struct
{
int CourseID[25];
char CourseName[100][25];
}Course;
void NewCourse(void);
#endif
My code
#include <stdio.h>
#include <stdlib.h>
#include "Homework.h"
void NewCourse()
{
int i;
int CNumber = 0;
Course storeC;
for(i = 0; i < 0; i++)
{
if(storeC.CourseID[i] == 0)
{
if(storeC.CourseName[i] == NULL)
{
int CNumber = i;
break;
}
}
}
printf("%d\n", CNumber);
printf("Please enter the course's ID number: ");
scanf("%d", &storeC.CourseID[CNumber]);
printf("Please enter the course's name: ");
scanf("%s", storeC.CourseName[CNumber]);
}
and my main does not really apply since the problem lies within storing the data.
A few things to keep in mind is I must utilize a separate file for my functions and I must use a header file for my structs.
I know my for loop to determine where in the array may not be effective, but I am not so worried about it as of right now.
My question is how do I store the data from this function to the
header file?
Update
I changed the main function to fit everything else and I end up with this error now.
a label can only be part of a statement and a declaration is not a
statement
The code in main is:
switch(Option)
{
case 1:
Course c = NewCourse();
printf("%d\n%s\n", c.CourseID[0], c.CourseName[0]); // For testing purposes
break;
What is causing the error because it says it stems from line 29 which is the Course c = NewCourse();?
Change NewCourse to return a Course.
Course NewCourse(void);
Change the implementation to:
Course NewCourse()
{
int i;
int CNumber = 0;
Course storeC;
...
return storeC;
}
Change main accordingly.
int main()
{
Course c = NewCourse();
}
PS
You said,
I cannot use struct arrays because I am not allowed to allocate memory.
I assume that to mean that you cannot use dynamic memory allocation. If you are allowed to create an array of structs in the stack, you can simplify your code by using:
typedef struct
{
int CourseID[25];
char CourseName[100];
}Course;
void NewCourse(Course course[]);
and in main, use:
Course courses[25];
NewCourse(courses)
In response to your update
You needed to add a scope block { } around the code as follows:
int main()
{
{
Course c = NewCourse();
}
}
This should resolve your error and allow your code to compile.
Additionally, you have an error in manipulating the CNumber Variable. It is declared twice, with different scopes:
int CNumber = 0; // the first definition with the scope of the NewCourse Function
Then inside the test, with a block scope:
if(storeC.CourseID[i] == 0)
{
if(storeC.CourseName[i] == NULL)
{
int CNumber = i; // block-scope. This is not the same CNumber Variable (todo: Omit int)
break;
}
}
As a result, when you reference it later in
printf("%d\n", CNumber);
printf("Please enter the course's ID number: ");
scanf("%d", &storeC.CourseID[CNumber]);
printf("Please enter the course's name: ");
scanf("%s", storeC.CourseName[CNumber]);
It will be always reference the function scope variable, which is always be zero.
Solution: omit the int declaration inside the test:
if(storeC.CourseName[i] == NULL)
{
CNumber = i;
break;
}
I have a struct person that has the following elements, defined in data.h
typedef struct person{
char firstName[20];
char familyName[20];
char telephoneNum[20];
int type; // 0 = student / 1 = employee;
}newPerson;
I created an array of person[MAX_PERSONS] that is initialized in my menu() function. I then have an addFirstName(newPerson pers) function. However when I try to test print format using my printFormat(newPerson pers)function, I get blank, instead of the inputted name.
I have included the menu(), addFirstname(newPerson pers), and printFormat(newPerson pers) function below. I was wondering if anyone could tell me the reason for this. Any help or pointers would be appreciated. Thank you in advance.
int menu(){
int num = 0;
newPerson person[MAX_PERSONS];
int option; // for user input for menu
printf("\n\tPlease choose one of the following options to continue (0-9): ");
scanf("%d", &option );
printf("\n\tYou selected %d\n", option);
if (option == 0){ //program will close
printf("\tProgram will now close.\n");
exit(1);
}
if (option == 1){ //program will ask for name input
addRecord(person[num]);
printFormat(person[num]);
char choice[0];
printf("\n\t\tWould you like to enter another record? (y/n): ");
scanf("%s", choice);
if (choice[0] == 'y'){
num++;
addRecord(person[num]);
}
if (choice[0] == 'n'){
num++;
mainMenu();
}
/*
IF YES, THEN NUM++
THEN RUN ADDRECORD(PERSONNUM) AGAIN.
IF NO, THEN RETURN TO MAIN MENU.
PRINTMENU
THEN RUN MENU AGAIN
*/
}
printf("\n\tNot a valid option, please try again // THE END OF MENU FUNCTION\n");
return 0;
}
void addFirstName(newPerson pers){
char firstName[20];
printf("\n\tEnter first Name: ");
scanf("%20s", firstName);
strcpy(pers.firstName, firstName);
printf("\n\tThe name entered is %s", pers.firstName);
}
void printFormat(newPerson pers){
printf("\t\tThe name is %s", pers.firstName);
}
It's because you pass the structure to addFirstName by value meaning that the function receives a copy of the structure. And changing a copy will of course not change the original.
While C does not support passing arguments by reference, it can be emulated using pointers. So change the addFirstName function to receive a pointer to the structure as its argument.
Your big problem is that you are passing structures by value instead of by pointers. This result in that you change copies of original objects inside your function addFirstName and not the original object. You should declare it as:
void addFirstName( newPerson* pers);
void printFormat( newPerson* pers);
Example:
#include <stdio.h>
void call_by_value(int x) {
printf("Inside call_by_value x = %d before adding 10.\n", x);
x += 10;
printf("Inside call_by_value x = %d after adding 10.\n", x);
}
int main() {
int a=10;
printf("a = %d before function call_by_value.\n", a);
call_by_value(a);
printf("a = %d after function call_by_value.\n", a);
return 0;
}
this will produce:
a = 10 before function call_by_value.
Inside call_by_value x = 10 before adding 10.
Inside call_by_value x = 20 after adding 10.
a = 10 after function call_by_value.