I'm kind of new to programming C with Code::Blocks(Version 12.11), started this semester in my college, but I manage.
I recently learned in class about pointers, memory allocation and dynamic arrays(none are my forte), and I incorporated them in my program(and it compiles)
Now the problem comes when I run the Program and go to Menu -> Add a Product, the program terminâtes when I input a price and I receive "Process Returned -1073741819 (0xc0000005)".
I did some research and found out it's an access violation but I don't really understand how to correct it.
Regards
Here's the code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define maxCharName 64
#define maxCharUserPass 8
#define maxCharId 5
// Product Structure
typedef struct{
char name[maxCharName];
char idCode[maxCharId];
float price;
float stock;
}product;
// DataBase of Products
typedef struct{
int sizeT;
product *array;
} TProducts;
TProducts a;
// Press any Key on the Keyboard to Proceed
void pressKeyToContinue(){
puts("\n\n\n Please Press any Key to Continue...");
getchar();
}
// Start Page
void startPage(){
puts("\n\n\n -- Welcome to WeePro Manager --\n\n");
puts(" -- Version 1.0 --\n\n\n\n");
puts(" -- Developped By: Nick --");
pressKeyToContinue();
system("cls");
}
// Program Terminator
void shutdown(){
puts("\n\n\n Good-Bye");
pressKeyToContinue(); // Awaits User Input
exit(0);
}
// Asks User Information for Verification
int userLogin(){
char userName[maxCharUserPass] = "WPuser";
char inputUserName[maxCharUserPass];
char passWord[maxCharUserPass] = "12345";
char inputPassWord[maxCharUserPass];
printf("Username? ");
scanf("%s",inputUserName); fflush(stdin);
printf("Password? ");
scanf("%s", inputPassWord); fflush(stdin);
system("cls");
if((strcmp(userName, inputUserName) == 0)&&(strcmp(passWord, inputPassWord) == 0)){
return 1;
}else{ return 0;}
}
// Lists All Products With their Respective Information
void listAll(){
int idx = 0;
puts("List:");
while((idx < a.sizeT)&&(a.array[idx].name != NULL)){
printf(":::%s ( id: %s )", a.array[idx].name, a.array[idx].idCode);
printf("Price: %6.2f eur/g", a.array[idx].price);
printf("Stock: %6.2f g", a.array[idx].stock);
idx++;
}
pressKeyToContinue();
system("cls");
}
// Input Product ID Code
char* inputIdCode(){
char* tempIdCode;
puts("ID Code?");
scanf("%s", tempIdCode);
system("cls");
return tempIdCode;
}
// Search By ID Code
int searchIdCode(){
int idx = 0;
char* tempIdCode;
tempIdCode = inputIdCode();
do{
if(strcmp(a.array[idx].idCode, tempIdCode) == 0){
return idx;
}else{
idx++;
}
}while(idx < a.sizeT);
puts("No Product With Such an ID Code!");
return -1;
}
// Input Product Name
char *inputProductName(int length){
char name[maxCharName];
puts("Product Name?");
scanf("%s", name); fflush(stdin);
system("cls");
return name;
}
// Input Product Price
float inputProductPrice(int length){
float price;
puts("Product Price?");
scanf("%f", price); fflush(stdin);
system("cls");
return price;
}
// Input Product Stock
float inputProductQuantity(int length){
float quantity;
puts("Product Stock?");
scanf("%f", quantity); fflush(stdin);
system("cls");
return quantity;
}
/////////////////
// Add Product //
/////////////////
// New Product Adder
void addProduct(){
char* tempStr;
float temp;
if(a.sizeT == 0){
a.sizeT = 1;
a.array = (product*)malloc((a.sizeT)*sizeof(product));
}else{
a.sizeT++;
a.array = (product*)realloc(a.array, (a.sizeT)*sizeof(product));
}
tempStr = inputProductName(a.sizeT);
strcpy(a.array[a.sizeT].name, tempStr);
temp = inputProductPrice(a.sizeT);
temp = inputProductQuantity(a.sizeT);
system("cls");
}
void transaction(){}
////////////////////
// Delete Product //
////////////////////
// Delete Product
void deleteProduct(){
int idx, idxPro;
char* tempIdCode;
puts("Delete Which Product?\n");
tempIdCode = inputIdCode();
idxPro = searchIdCode(tempIdCode);
idx = idxPro + 1;
while(idx < a.sizeT){
a.array[idx] = a.array[idx+1];
idx++;
}
a.array = realloc(a.array, (a.sizeT-1)*sizeof(product));
}
//Product Information Modifier
void modifyProduct(){
char choice;
int tabLength;
do{
puts("Modify What?\n");
puts(" -> [N]ame\n");
puts(" -> [P]rice\n");
puts(" -> [S]tock\n\n");
puts(" -> [R]eturn to Previous Menu"); // Prints the Menus' Options
scanf("%c", &choice);
choice = toupper(choice); // Save Users' Choice And Up Case
fflush(stdin);
switch(choice){
case 'N':
system("cls");
tabLength = searchIdCode();
inputProductName(tabLength);
break;
case 'P':
system("cls");
tabLength = searchIdCode();
inputProductPrice(tabLength);
break;
case 'S':
system("cls");
tabLength = searchIdCode();
inputProductQuantity(tabLength);
break;
case 'R':
system("cls");
returnToMenu2();
break;
default:
puts("Something Went Wrong!\n");
pressKeyToContinue();
system("cls");
}
}while(choice != 'o');
}
// Sub-Menu Interface
void menu(){
char choice;
do{
puts("Please Make Your Selection.\n");
puts(" -> [A]dd a New Product\n");
puts(" -> [M]odify a Product\n");
puts(" -> [D]elete a Product\n\n");
puts(" -> [R]eturn to Main Menu"); // Prints the Menus' Options
scanf("%c", &choice); fflush(stdin);
choice = toupper(choice); // Save Users' Choice And Up Case
switch(choice){
case 'A':
system("cls");
addProduct();
break;
case 'M':
system("cls");
modifyProduct();
break;
case 'D':
system("cls");
deleteProduct();
break;
case 'R':
system("cls");
returnToMenu1();
break;
default:
puts("Something Went Wrong!\n");
pressKeyToContinue();
system("cls");
}
}while(choice != 'o');
}
// Return To Ma
> Blockquote
in Menu
void returnToMenu2(){
menu();
}
// Main Menu
void controlPanel(){
char choice;
do{
puts("Please Make Your Selection.\n");
puts(" -> [T]ransaction\n");
puts(" -> [M]enu\n");
puts(" -> [L]ist\n");
puts(" -> [S]hutdown"); // Prints the Panels' Options
scanf("%c", &choice); fflush(stdin);
choice = toupper(choice); // Save Users' Choice And Up Case
switch(choice){
case 'T':
system("cls");
transaction();
break;
case 'M':
system("cls");
menu();
break;
case 'L':
system("cls");
listAll();
break;
case 'S':
system("cls");
shutdown();
break;
default:
puts("Something Went Wrong!\n");
pressKeyToContinue();
system("cls");
}
}while(choice != 'o');
}
// Return To Main Menu
void returnToMenu1(){
controlPanel();
}
int main(){
int loginSuccess=1;
//loginSuccess = userLogin();
switch(loginSuccess){
case 0:
shutdown();
break;
case 1:
startPage();
controlPanel();
break;
}
}
An attempt is being made to write to randon memory, via the uninitialized pointer tempIdCode:
char* inputIdCode(){
char* tempIdCode;
puts("ID Code?");
scanf("%s", tempIdCode);
system("cls");
return tempIdCode;
}
You need to allocate memory for tempIdCode before attempting to write to it. You must use malloc() here (and not return the address of a local array):
char* tempIdCode = malloc(20);
if (tempIdCode)
{
/* The format specifier "%19s" instructs scanf()
to read at most 19 characters, one less than
allocated to allow for terminating null character
written by scanf(), to prevent potential buffer
overrun. */
scanf("%19s", tempIdCode);
}
The caller of the function must explicitly check for a return NULL pointer. The caller must also free() the allocated memory.
This is a killer:
// Input Product Name
char *inputProductName(int length){
char name[maxCharName];
puts("Product Name?");
scanf("%s", name); fflush(stdin);
system("cls");
return name;
}
The reference returned by this function points to an already freed block of memory on the stack, as char name is only valid as long the program is inside the function name is declared in.
When leaving the function name is freed automagically, so any dereferencing of the function's result leads to UB, as it most propably will be accessing unallocated memory.
To solve this you might like to pass in a buffer, where to read the data into:
// Input Product Name
char * inputProductName(int length, char * name){
puts("Product Name?");
scanf("%s", name); fflush(stdin);
system("cls");
return name;
}
and call it like this:
// New Product Adder
void addProduct(){
char* tempStr;
float temp;
if(a.sizeT == 0){
a.array = malloc((a.sizeT)*sizeof(product));
}else{
a.array = realloc(a.array, (a.sizeT)*sizeof(product));
}
a.sizeT++;
inputProductName(a.sizeT, a.array[a.sizeT].name);
...
Related
Im programming a tiny music player for school project. And our teacher tell us we have to use linked list.
But i have this crash in my program without warnings, my function Afficher_Liste is working fine (its a function to view my linked list)
My structure which define a music
typedef struct Piste{
char *pTitle;
char *pArtist;
char *pPath;
struct Piste *pNext;
struct Piste *pPrev;
}Piste;
My function :
void Play_Music(Piste **pHead){
int choice;
int ctr = 1;
char * path_music;
path_music= (char*)malloc(200 * sizeof(char));
View_List(&ppDL);
Piste *pCur = *pHead;
printf("What music you want to play ?");
scanf("%d",&choice);
while(choix!=cptr){
pCur = pCur->pNext;
ctr++;
if(choice==cptr){
path_music= pCur->pPath;
}
}
printf("your choice is %s",path_music);
scanf("%d",choice);
}
Edit : the call of the function
void User_Mode(){
int choice;
char *search= NULL;
while(choice!= 4)
{
system("cls");
printf("---------- User Menu----------\n\n");
printf("1 - Search\n");
printf("2 - Play a music\n");
printf("3 - Back to menu\n");
printf("your choice?\n");
scanf("%d", &choice);
switch(choice){
case 1:
fflush(stdin);
search = (char*)malloc(200 * sizeof(char));
printf( "what do you want to listen ? : \n" );
scanf( "%[^\n]", seach);
fgetc( stdin );
if(search!=NULL){
search_music(search,&ppDL);
}
break;
case 2:
play_music();
break;
case 3:
main_menu();
break;
default:
system("cls");
printf("your choice isnt good\n\n");
user_mode();
}
}
}
Edit2 : tried to translate my code
Change your case statement to
case 2:
play_music( &ppDL );
break;
Im basically Writing a program that creates, reads, updates and
deletes records in a binary file.
Everything compiles correctly, no syntax errors, but I do have some
bugs.
KNOWN BUGS
1.) Imputing any strings does not work, using fgets
2.) Ctrl-D Does Work but outputs a 'default' error before it exits.
3.) Update does not work (Not my main issue at the moment as the others are more important for now.)
4?) I'm not sure if the menu is working how it's supposed to work. I
think the do while is correct, since in the menu if I select and hit
CTRL-D it does exit the program. Just wanna be sure.
Right now I just want to know why, It is skipping the courseName in
the inputs function.
Here is my code thus far
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <errno.h>
#include <string.h>
typedef struct{
char courseName [64];
char courseSched [4];
unsigned int courseHours;
unsigned int courseSize;} COURSE;
FILE *pfileCourse;
int courseNumber = 0;
//Prototypes
void inputDetails(COURSE *c);
void readCourseRecord();
void createCourseRecord();
void print_menu();
void modifyCourseInfo();
void deleteCourse();
void display(COURSE c);
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
int main(int argc, char *argv[]) {
char choice; // this is the choice
printf("Enter one of the following actions or press CTRL-D to exit\n");
printf("C - Create a new course record\n");
printf("R - Read an existing course record\n");
printf("U - Update an existing course record\n");
printf("D - Delete an existing course record\n");
do{
choice = getchar();
switch(choice) {
case 'c':
case 'C':
printf("YOU PICKED C for Create\n");
createCourseRecord();
break;
case 'r':
case 'R':
printf("This is Choice R\n");
readCourseRecord();
break;
case 'u':
case 'U':
printf("Here is where you update an existing course\n");
modifyCourseInfo();
break;
case 'd':
case 'D':
printf("here is where you Delete an existing course record\n");
deleteCourse();
break;
default:
printf("Wrong Choice!\n");
}
}while(choice != EOF);
return 0;
}
void createCourseRecord() {
COURSE data;
pfileCourse = fopen("courses.dat", "ab");
printf("Please Enter The Details of The Course\n");
inputDetails(&data);
fwrite(&data, sizeof(data), 1, pfileCourse);
fclose(pfileCourse);
printf("Course Has Been Created!\n");
}
void inputDetails(COURSE *c) {
printf("Enter a course number: \n");
scanf("%d", &courseNumber);
printf("Enter a Course Name: \n");
fgets(c->courseName, sizeof(courseName), stdin);
printf("Enter the course schedule (MWF or TR): \n");
fgets(c->courseSched, 4, stdin);
fflush(stdin);
printf("Enter the course credit hours: \n");
scanf("%d",&c->courseHours);
fflush(stdin);
printf("Enter Number of Students Enrolled: \n");
scanf("%d",&c->courseSize);
return;
}
void readCourseRecord(){
COURSE data;
int flag = 0;
int readCourseNumber = 0;
printf("Please Enter a Course Number to Display\n");
scanf("%d", &readCourseNumber);
fflush(stdin);
pfileCourse = fopen("courses.dat", "rb");
while((fread(&data, sizeof(data), 1, pfileCourse)) > 0) {
if(readCourseNumber == courseNumber)
{
display(data);
flag = 1;
}
}
fclose(pfileCourse);
if(flag == 0)
printf("Course not Found!\n");
}
void deleteCourse(){
int newCourseNum;
COURSE data;
FILE *file2;
printf("Please Enter The Course You Wish You Delete\n");
scanf("%d", &newCourseNum);
pfileCourse = fopen("courses.dat", "rb");
file2 = fopen("temp.dat", "wb");
rewind(pfileCourse);
while((fread(&data, sizeof(data), 1, pfileCourse)) > 0)
{
if(courseNumber != newCourseNum)
{
fwrite(&data, sizeof(data), 1, file2);
}
}
fclose(file2);
fclose(pfileCourse);
remove("courses.dat");
rename("temp.dat", "courses.dat");
printf("%d was Successfully deleted\n", newCourseNum);
}
void modifyCourseInfo()
{
COURSE data;
int newCourseNum, found = 0;
printf("Modify\n");
printf("Please Enter The Course You Wish You Modify\n");
scanf("%d", &newCourseNum);
pfileCourse = fopen("courses.dat", "rb+");
while ((fread(&data, sizeof(data), 1, pfileCourse)) > 0 && found == 0)
{
if (courseNumber == newCourseNum)
{
display(data);
printf("Please Enter New Details\n");
inputDetails(&data);
fseek(pfileCourse, - (long)sizeof(data), 1);
fwrite(&data, sizeof(data), 1, pfileCourse);
printf("Course Updated\n");
found == 1;
}
}
fclose(pfileCourse);
if(found == 0)
printf("ERROR: course not found\n");
}
void display(COURSE c){
printf("courseNumber:\t %d\n", courseNumber);
printf("courseName:\t %s\n",c.courseName);
printf("courseSched:\t %s\n",c.courseSched);
printf("courseName:\t %d\n",c.courseHours);
printf("courseSize:\t %d\n",c.courseSize);
}
It doesn't skip courseName, courseName just gets value '\n' because scanf function stops reading your input BEFORE white space. Scanf ignores any whitespace characters encountered before the next non-whitespace character. So you can just add
scanf("%d[^\n]", &courseNumber);
getchar();
after every scanf you have but I'd recommend you to use fgets function for every interactive input.
I'm trying to write a simple phone book program. I have completed the first function and according to I observe it works without error. However, in second function (which is ""display()"") I can't show to user after I enter person knowledge. I'm working with binary mode. What the problem is in second function I couldn't understand. If you examine and help I'll be satisfied. Thanks in advance.
#include <stdio.h>
#include <stdlib.h> // "stdlib" library contains of exit() function
#include <malloc.h> // "malloc" library contains of malloc() function
#include <Windows.h> // "Windows" library contains of Sleep() function which waits the system as you want
#include <io.h> // "io" library contains of filelength() function
struct personKnowledge
{
char name[32];
char surname[32];
char number[32];
};
FILE *ptrFILE,*ptrFILE1;
long int recordLength,totalRecordLength,location;
static int counter = 0;
int number,totalRecordNumber;
void newRecord();
void display();
void deletE();
void add();
void update();
int main()
{
int choice;
do
{
printf("\n\t\t --- Phone Book Program ---");
printf("\n\n\t\t 1) New record"); // The options are being presented to user
printf("\n\n\t\t 2) Display person knowledge");
printf("\n\n\t\t 3) Delete someone");
printf("\n\n\t\t 5) Update person knowledge");
printf("\n\n\t\t 6) Exit");
printf("\n\n\nEnter your choice: ");
scanf("%d", &choice);
switch (choice)
{
case 1:
{
newRecord();
break;
}
case 2:
{
display();
break;
}
case 3:
{
break;
}
case 4:
{
break;
}
case 5:
{
break;
}
case 6:
{
printf("\nWorking has been completed.\n");
return 0;
}
default:
{
printf("\nWrong entry! The program has been terminated.\n");
break;
}
}
} while (choice >= 1 && choice <= 6);
return 0;
}
void newRecord()
{
if ((ptrFILE = fopen("Phone Book.dat", "wb")) == NULL)
{
printf("The file couldn't open\n");
exit(0);
}
system("cls"); // Screen is being cleaned
struct personKnowledge *p; // p means person
p = (struct personKnowledge *)malloc(sizeof(struct personKnowledge)); // Memory is being allocated
fflush(stdin);
recordLength = sizeof(p); // size of p
printf("|| For the %d. person ||\n", counter+1);
printf("\n\Express person name: "); // User is entering the person's knowledge and they are being saved in file
gets(p->name);
printf("Express %s's surname: ", p->name);
gets(p->surname);
printf("Express %s's number: ", p->name);
gets(p->number);
fwrite(&(*p), recordLength, 1, ptrFILE);
printf("\nPlease wait, information is saving to file..\n");
Sleep(750);
printf("*-* Saving operation has been completed succesfully. *-*\n");
free(p);
counter++;
fclose(ptrFILE);
}
void display()
{
if ((ptrFILE = fopen("Phone Book.dat", "rb")) == NULL)
{
printf("The file couldn't open\n");
exit(0);
}
system("cls"); // Screen is being cleaned
struct personKnowledge *s; // s means searching
s = (struct personKnowledge *)malloc(sizeof(struct personKnowledge));
fflush(stdin);
recordLength = sizeof(s);
totalRecordLength = filelength(fileno(ptrFILE));
totalRecordNumber = totalRecordLength / recordLength;
printf("\n\nExpress person record number which you search: ");
scanf("%d", &number);
location = (number - 1)*recordLength;
fseek(ptrFILE, location, SEEK_SET);
fread(&(*s), recordLength, 1, ptrFILE);
printf("\n*-* Person knowledge which you search *-*\n");
Sleep(750);
printf("Name: %s\n", s->name);
printf("Surname: %s\n", s->surname);
printf("Number: %s\n", s->number);
free(s);
fclose(ptrFILE);
}
recordLength = sizeof(p);
is wrong, this is the size of the pointer which is normally 4 on a 32 bit system and 8 on a 64 bit syste.
you need
recordLength = sizeof(*p);
or
sizeof(struct personKnowledge);
which gives you the size of the structure pointed by p.
The 1. and 3. menu items are working, but if I choose the 2. menu item it's not listing my data. Why is that?
(It has to be compiled and run in linux command line [NO IDE!])
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <time.h>
struct log{
int id;
char name[20];
char location[20];
int quantity;
char quantity_type[10];
time_t added;
};
char fname[] = "data2.dat";
void add();
void listAll();
int nextId();
int main(){
int ch;
while(1){
system("clear");
printf("///Log stuff!///\n\n");
printf("1. Add\n");
printf("2. List all\n");
printf("0. Exit\n");
printf("\n///////////////////////////////\n\n");
printf("Choose a number from the menu: ");
scanf("%d", &ch);
switch(ch){
case 1: add();
break;
case 2: listAll();
break;
case 0: exit(0);
break;
}
}
return 0;
}
void add(){
FILE *f;
struct log log;
f = fopen(fname, "ab");
if(f == NULL){perror("Can't open!\n");}
log.id = nextId();
printf("\nName: ");
scanf("%s", log.name);
printf("\nLocation: ");
scanf("%s", log.location);
printf("\nQuantity: ");
scanf("%d", &log.quantity);
printf("\nQuantity type: ");
scanf("%s", log.quantity_type);
log.added = time(NULL);
fwrite(&log,sizeof(log),1,f);
fclose(f);
}
void listAll(){
FILE *f;
struct log log;
f = fopen(fname,"rb");
if(f == NULL){perror("Can't open!\n");exit(1);}
printf("\n///////////////////////////////\n\n");
printf("\tList of all data\n\n");
printf("///////////////////////////////\n\n");
while(fread(&log,sizeof(log),1,f) == 1){
printf("%d\t",log.id);
printf("%s\t",log.name);
printf("%s\t",log.location);
printf("%d\t",log.quantity);
printf("%s\t",log.quantity_type);
printf("%s",ctime(&log.added));
}
printf("\n///////////////////////////////\n\n");
fclose(f);
}
int nextId(){
FILE *f;
struct log log;
int id = 1;
f = fopen(fname, "rb");
if(f == NULL){perror("Can't open!\n");}
while(!feof(f)){
fread(&log, sizeof(log), 1, f);
if(log.id >= id){id = log.id + 1;}
}
fclose(f);
return id;
}
Is there a more elegant way to do this task?
This menu display/input choice/switch section of the code has a logic error
the screen is being cleared before the user has a chance to look at any displayed data.
Proper placement of calls to system(clear) and getchar() will fix the problem
a function should only have 1 normal exit. Any other exit points should be only for error conditions
You might try the following:
system(clear);
int done = 0;
while( !done )
{
printf("///Log stuff!///\n\n");
printf("1. Add\n");
printf("2. List all\n");
printf("3. Exit\n");
printf("\n///////////////////////////////\n\n");
printf("Choose a number from the menu: ");
if( 1 != scanf("%d", &ch) )
{ // then scanf failed
perror( "scanf for menu choice failed" );
exit( EXIT_FAILURE );
}
// implied else, scanf successful
// eliminate menu from screen
system(clear);
switch(ch)
{
case 1:
add();
break;
case 2:
listAll();
printf( "\npress any key to continue\n" );
getchar();
break;
case 3:
done=1;
break;
default:
printf("\nyou entered an invalid menu selection, try again\n");
break;
} // end switch
} // end while
static stack implementation
this is also not deleting according to the lifo principle
static stack implementation:
it is not taking name for the second time
this is the new code now tell me why is it not working
please help
typedef struct student {
char name[20];
int roll;
int age;
} mystruct;
#define size 40
int top;
static mystruct s[size];
void push()
{
if (top == size - 1) {
printf("\noverflow"); //
} else {
printf("\nenter the name of the student");
gets(s[top].name);//not taking name for d 2 time
printf("\nenter the roll number");
scanf("%d", &s[top].roll);
printf("\nenter the age of the student");
scanf("%d", &s[top].age);
++top;
}
}
void pop()
{
if (top == -1)
{
printf("\nunderflow");
} else {
printf("%s", s[top].name);
printf("%d", s[top].roll);
printf("%d", s[top].age);
printf("\npopped");
--top;
}
}
void display()
{
int i;
if (top == -1) {
printf("\nstack is empty");
} else {
for (i = top; i > 0; i--) {
printf("\nthe name of the student is%s", s[top].name);
}
printf("\nthe roll no of the student is%d", s[top].roll);
printf("\nthe age of the student is%d", s[top].age);
}
}
main()
{
top = -1;
char ch;
while (1) {
printf("\nwelcome to static stack menu");
printf("\n1.PUSH\n2.POP\n3.DISPLAY\n0.EXIT");
printf("\nplease enter your choice\n");
ch = getche();
if (ch == '0') {
break;
}
switch (ch) {
case '1':
push();
break;
case '2':
pop();
break;
case '3':
display();
break;
default:
printf("choice not valid");
break;
}
}
}
The first problem I noticed was that top is initialized to -1. Trying to access the member data of s[top] when top is initialized to -1 will result in unpredictable behavior.
I would suggest changing the line
top = -1;
to
top = 0;
That changes the basic assumption you have made in push, pop, and display about when the stack is empty and when it is full. Instead of checking if ( top == -1 ), you have to now check if (top == 0 ). Instead of checking if ( top == size - 1 ), you have to now check if ( top == size ).
In pop, you have to use top-1 instead of top.
The for loop in display is not scoped correctly. You need to use:
for (i = top-1; i >= 0; i--) {
printf("\nthe name of the student is %s", s[i].name);
printf("\nthe roll no of the student is %d", s[i].roll);
printf("\nthe age of the student is %d", s[i].age);
}
Also, reading the options for the menu and reading the subsequent input is little bit tricky.
After you read the menu option, you have to make sure that you eat up all the input until the next newline. Otherwise, gets() will read everything after your menu option until the end of the line. If you typed 1 for the menu and then typed Return/Enter, the name will be automatically accepted as "\n". Hence, I suggest the lines:
printf("\nwelcome to static stack menu");
printf("\n1.PUSH\n2.POP\n3.DISPLAY\n0.EXIT");
printf("\nplease enter your choice\n");
ch = fgetc(stdin);
/* Skip till the end of line is read. */
while ( fgetc(stdin) != '\n' );
Also, after you read the age of the object, you have to eat everything up to the newline. Otherwise, the newline character is read in as the choice for the next menu option.
scanf("%d", &s[top].age);
/* Skip till the end of line is read. */
while ( fgetc(stdin) != '\n' );
Here's the fully working file. I have replaced gets by fgets and getche by fgetc.
#include <stdio.h>
#include <string.h>
typedef struct student {
char name[20];
int roll;
int age;
} mystruct;
#define size 40
int top;
static mystruct s[size];
void push()
{
if (top == size) {
printf("\noverflow"); //
} else {
printf("\nenter the name of the student: ");
fgets(s[top].name, 20, stdin);//not taking name for d 2 time
// The newline character is part of s[top].name when fgets is
// finished. Remove that.
s[top].name[strlen(s[top].name)-1] = '\0';
printf("\nenter the roll number: ");
scanf("%d", &s[top].roll);
printf("\nenter the age of the student: ");
scanf("%d", &s[top].age);
/* Skip till the end of line is read. */
while ( fgetc(stdin) != '\n' );
++top;
}
}
void pop()
{
if (top == 0)
{
printf("\nunderflow");
} else {
printf("%s, ", s[top-1].name);
printf("%d, ", s[top-1].roll);
printf("%d", s[top-1].age);
printf("\npopped");
--top;
}
}
void display()
{
int i;
if (top == 0) {
printf("\nstack is empty");
} else {
for (i = top-1; i >= 0; i--) {
printf("\nthe name of the student is %s", s[i].name);
printf("\nthe roll no of the student is %d", s[i].roll);
printf("\nthe age of the student is %d", s[i].age);
}
}
}
main()
{
top = 0;
char ch;
while (1) {
printf("\nwelcome to static stack menu");
printf("\n1.PUSH\n2.POP\n3.DISPLAY\n0.EXIT");
printf("\nplease enter your choice\n");
ch = fgetc(stdin);
/* Skip till the end of line is read. */
while ( fgetc(stdin) != '\n' );
if (ch == '0') {
break;
}
switch (ch) {
case '1':
push();
break;
case '2':
pop();
break;
case '3':
display();
break;
default:
printf("choice, %c, not valid", ch);
break;
}
}
}
You need to change getche() to getchar()
Note: getche() is a non-standard function.
Maybe this will be useful http://www.delorie.com/djgpp/doc/libc/libc_385.html
Pay attention to implementation note:
"If you can detect the situation when one of the conio functions is called for the very first time since program start, you could work around this problem by calling the gppconio_init function manually"
or just replace it with getchar(). And there meaned conio included.