I've been working on a group program for a systems programming class which will run functions that someone at a bank would use. These functions include add bank customers, output balance of a customer, and so on. The problem lies with the add customer function.
This function will run in an infinite loop in terminal and Putty, but when I run it as a standalone program in XCode the loop quits. Is there anything wrong with the program that I, my group members AND our professor are overlooking?
#include <stdio.h>
#include <string.h>
#include "./bank.h"
void add(FILE *fp)
{
int i=0;
char firstName[20];
char lastName[20];
float camount;
int prompt;
float samount;
float mamount;
fseek(fp,0,2);
do
{
printf("\nEnter first name: ");
scanf("%s", firstName);
strcpy(bank[i].firstName, firstName);
printf("\nEnter last name: ");
scanf("%s",lastName);
strcpy(bank[i].lastName, lastName);
printf("\nEnter checking account balance: ");
scanf("%f", &camount);
bank[i].checking = camount;
printf("\nEnter savings account balance: ");
scanf("%f", &samount);
bank[i].savings = samount;
printf("\nEnter money market account balance: ");
scanf("%f", &mamount);
bank[i].moneyMarket = mamount;
fwrite(&bank[i],1, sizeof(struct BankInfo),fp);
i++;
printf("Enter 1 to enter another name and 0 to quit: ");
scanf("%d", &prompt);
printf("%d\n", prompt);
} while(prompt == 1);
fclose(fp);
return;
}
Screenshot of output once Makefile is executed:
Sidenote: This function does write onto the file that we are passing which is great but we still need for it to break out of the loop.
EDIT: code for the main function:
#include
#include
#include
#include "bank.h"
#include "definitions.h"
int main()
{
FILE *fp;
int selection;
fp=fopen("bankInfo.dat","ab+");
selection=menu();
while(selection !=6)
{
switch(selection)
{
case 1:
add(fp);
break;
case 2:
// outputBalance(fp);
break;
case 3:
delete(fp);
break;
case 4:
update(fp);
break;
case 5:
// display(fp);
break;
case 6:
exit(0);
break;
default:
printf("Invalid selection\n");
break;
}
}
fclose(fp);
return 0;
}
You are assigning selection only once. This should fix your issue:
while(true)
{
selection=menu();
switch(selection)
{
case 1:
add(fp);
break;
case 2:
// outputBalance(fp);
break;
case 3:
delete(fp);
break;
case 4:
update(fp);
break;
case 5:
// display(fp);
break;
case 6:
fclose(fp);
exit(0);
break;
default:
printf("Invalid selection\n");
break;
}
}
return 0;
Related
I want to make a menu that classifies animals into insects, birds, mammals and fishes with specific characteristics for each of these (using composite variables). I thought I'd use a nested switch case(one switch for the category of the animals and another switch for each category to perform the actions). The problem is, after I've entered a new entry for instance, I wanna have the option to go back and pick another action or even go back and pick another category. How can I do that? I tried with a do-while but I'm just getting an endless loop.
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
typedef struct{
unsigned int noLegs, lifeSpan;
char *name;
}insect;
typedef struct{
float speed, length;
char *habits, *name;
}bird;
typedef struct{
float weight, height;
char *food, *name;
}mammal;
typedef struct{
float weight, depth, salt;
char *name;
}fish;
int main(int argc, char **argv)
{
char choice, action;
bool running = true;
bool returnBack = true;
insect *i = (insect *)malloc(sizeof(insect));
if(!i)
{
printf("Failed to allocate memory.\n");
return -1;
}
while(running)
{
printf("Please choose a category:\n");
printf("1. Insects\n2. Birds\n3. Mammals\n4. Fishes\n5. Exit\n");
scanf(" %c", &choice);
switch(choice)
{
case '1':
printf("You've chosen: Insects\n");
while(returnBack)
{
printf("Please choose an action:\n");
printf("a. Add entry\nb. Delete entry\nc. Replace entry\nd. Lookup entries\ne. Back\n");
scanf(" %c", &action);
switch(action)
{
case 'a':
printf("What entry would you like to add?\n");
i->name = (char *)malloc(sizeof(char));
scanf("%s", i->name);
printf("How many legs does a %s have?\n", i->name);
scanf("%u", &(i->noLegs));
printf("What is the lifespan of a %s?\n", i->name);
scanf("%u", &(i->lifeSpan));
break;
case 'b':
printf("Which entry would you like to delete?\n");
break;
case 'c':
printf("Which entry would you like to replace?\n");
break;
case 'd':
printf("Which entry would you like to replace?\n");
break;
case 'e':
returnBack = false;
break;
default:
printf("Invalid action.\n");
}
}
break;
case '2':
printf("You've chosen: Birds\n");
break;
case '3':
printf("You've chosen: Mammals\n");
break;
case '4':
printf("You've chosen: Fishes\n");
break;
case '5':
running = false;
break;
default:
printf("Invalid choice.\n");
}
}
return 0;
}
As said by alex01011, you just need a while over the whole switch
When the user selects 5 running becomes FALSE and the loop exits.
One thing though, you forgot to clear the whitespace in the first scanf()
#include <stdio.h>
#include <stdlib.h>
#define TRUE (1==1)
#define FALSE (!TRUE)
/* ...
* ALL THE STRUCTS
*/
int main(int argc, char **argv)
{
char choice, action, running = TRUE;
insect *i = (insect *)malloc(sizeof(insect));
// CHECK ON MALLOC RETURN
while(running)
{
printf("Please choose a category:\n");
printf("1. Insects\n2. Birds\n3. Mammals\n4. Fishes\n5. Exit\n\n");
scanf(" %c", &choice); // <-- The leading space was missing
switch(choice)
{
/* ...
* PREVIOUS CASES
*/
case '5':
running = FALSE;
break;
default:
printf("Invalid choice.\n");
}
}
return 0;
}
---------- > ## Heading ## > when i input a character as an input default case of switch doesn't encounter and loop started > infinite times > > > enter code here
#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
void create();
void display();
void search();
struct node {
int data;
struct node* link;
};
struct node* head;
int main()
{
int value;
while (1) {
printf("Enter Correct Choice :- \n");
printf("Enter 1 to Create Linklist :- \n");
printf("Enter 2 to Display Linklist :- \n");
printf("Enter 3 to Search Linklist :- \n");
printf("Enter Your Choice Here _________ ");
scanf(" %d", &value);
switch (value) {
case 1:
create();
break;
case 2:
display();
break;
case 3:
search();
break;
default:
printf("Error !! Wrong Choice :- \n");
break;
}
}
return 0;
}
TL;DR- Always check the return value of scanf() for success.
In case of a non-numeric character input, the format specifier %d does not find a match, and no input is consumed (i.e., the invalid input remains in the input buffer). Thus, the switch body executes, most likely it does not find a match with any existing case statement, so the default case statement(s) get executed, and control goes back to while loop.
Then, due to the presence of the invalid input in the buffer (and not getting consumed), the above phenomena keeps on repeating.
The major problem is, in case of scanf() failure, the value of variable value remains uninitialized and indeterminate. It does not construct a well-defined program.
Couple of things:
Always initialize local variables.
Always check for success of scanf() before using the returned value, if you have to use scanf(). For better use fgets() to take user input.
In case of failure of input using scanf(), clean up the input buffer before trying to read next input.
The break causes the program to exit the switch case but not the while. To wxit the while as well you should do something like this:
#include <stdio.h>
#include <stdlib.h>
int main()
{
int value;
int done = 0;
while (!done) {
printf("Enter Correct Choice :- \n");
printf("Enter 1 to Create Linklist :- \n");
printf("Enter 2 to Display Linklist :- \n");
printf("Enter 3 to Search Linklist :- \n");
printf("Enter Your Choice Here _________ ");
scanf(" %d", &value);
switch (value) {
case 1:
printf("do stuff\n");
break;
case 2:
printf("do stuff\n");
break;
case 3:
printf("do stuff\n");
break;
default:
printf("Error !! Wrong Choice :- \n");
done = 1;
break;
}
}
return 0;
}
Here I used a variable initialized to 0 which indicates that the operation is not completed yet. When it's time to exit, the variable is set to 1, which causes the program to exit the while loop
Also, always remember to check the return value of printf(), to avoid possible errors
There is no break condition for while().
#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
void create();
void display();
void search();
struct node {
int data;
struct node* link;
};
struct node* head;
int main()
{
int value = 1;
while (value) {
printf("Enter Correct Choice :- \n");
printf("Enter 1 to Create Linklist :- \n");
printf("Enter 2 to Display Linklist :- \n");
printf("Enter 3 to Search Linklist :- \n");
printf("Enter 0 to exit :- \n");
printf("Enter Your Choice Here _________ ");
scanf(" %d", &value);
switch (value) {
case 1:
create();
break;
case 2:
display();
break;
case 3:
search();
break;
default:
printf("Error !! Wrong Choice :- \n");
break;
}
}
return 0;
}
if a non valid integer is enter for scanf(" %d", &value); value is not set and the invalid input is not flush => scanf will never block nor update value
you need to check scanf returns 1 (you read 1 value) and if not to flush the invalid input for instance reading all the line
so you can replace
scanf(" %d", &value);
switch (value) {
...
}
by
if (scanf("%d", &value) != 1) {
puts("invalid input");
while ((value = getchar()) != '\n') {
if (value == EOF) {
puts("EOF, exit");
exit(-1);
}
}
}
else {
switch(value) {
...
}
}
of course you can also manage the invalid input in your default case forcing an invalid value :
if (scanf("%d", &value) != 1) {
while ((value = getchar()) != '\n') {
if (value == EOF) {
puts("EOF, exit");
exit(-1);
}
}
value = -1; /* any value except 1,2 or 3 */
}
switch(value) {
...
}
Out of that you have no option to stop the execution, you can do :
...
puts("Enter 4 to exit :-);
...
switch (value) {
...
case 4:
exit(0);
...
}
I belive your intention is to run the program as long as "0" is not entered, but ter is no case for "0". also when we have scanf for %d and entering a "char" instead scanf will not read the char from buff. data on value will not get changed and it will keep printing existing data. (garbage if we enter invalid data first time itself, or any entered data.)
used fgets to read the input data, and do a scanf from buf, even when data is incorrect we are clearing the std input. so program will not get in to a infinite loop with scanf failure.
initilised "value = 0"
added case for "0".
scanf is replaced with fget +sscanf
#include <stdio.h>
#include <stdlib.h>
int main()
{
int value = 0;
char buff[256] = {0};
while (1) {
value = -1;
printf("Enter Correct Choice :- \n");
printf("Enter 1 to Create Linklist :- \n");
printf("Enter 2 to Display Linklist :- \n");
printf("Enter 3 to Search Linklist :- \n");
printf("Enter Your Choice Here _________ ");
fgets(buff, 255, stdin);
sscanf(buff, "%d", &value);
switch (value) {
case 1:
//create();
printf("case : 1\n");
break;
case 2:
//display();
printf("case : 2\n");
break;
case 3:
//search();
printf("case : 3\n");
break;
case 0 :
printf("case : 0 : Exiting program\n");
return 0;
default:
printf("Error !! Wrong Choice :- %d\n", value);
break;
}
}
return 0;
}
I am trying to make a simple option menu that is executed within a do- while loop. The menu has 5 different options. I am currently trying to test the the get initial option but when I choose the case 'b' the function does not even execute and the option menu reappears again
#include "mathprogram.h"
int main (void)
{
char menu_option,initials;
int difficulty;
printf(" EDUCATIONAL MATH PROGRAM!!!\n");
printf("------------------------------------------\n\n");
do{
printf("Main Menu\n");
printf("a. Learn about how to use program.\n");
printf("b. Enter your initials (3 individual letters).\n");
printf("c. Difficulty Selection.\n");
printf("d. Start a new sequence of problems.\n");
printf("e. Save and quit.\n");
printf(" Please enter an option from the main menu: ");
scanf("%c",&menu_option);
switch(menu_option){
case 'a':
//Learn_to_use();
break;
case 'b':
initials=get_intials();
break;
case'c':
printf("case c");
//difficulty = get_difficulty();
break;
case'd':
break;
case'e':
break;
default:
printf("invalid input");
break;
}
}while(menu_option !='e');
}
get initials function:
#include "mathprogram.h"
char get_intials(void){
char initails;
printf("Please Enter Initials: ");
scanf("%c",&initails);
return initails;
}
scanf("%c", &var);
leaves the newline in the buffer or stream.
Try to change it to
scanf(" %c", &var);
and it should work as expected (Note the space before the %; this consumes the whitespace so that the next scanf call should work).
However, the initials as defined in your program consist of only one character, not three. I'll leave that up to you to design, that is a different question.
There's a '\n' between option 'b' and the initials char, the "scanf" must handle it.
Complete code that works:
#include <stdio.h>
char get_intials(void){
char initails;
printf("Please Enter Initials: ");
scanf("\n%c",&initails) ;
return initails;
}
int main (void)
{
char menu_option,initials;
int difficulty;
printf(" EDUCATIONAL MATH PROGRAM!!!\n");
printf("------------------------------------------\n\n");
do{
printf("Main Menu\n");
printf("a. Learn about how to use program.\n");
printf("b. Enter your initials (3 individual letters).\n");
printf("c. Difficulty Selection.\n");
printf("d. Start a new sequence of problems.\n");
printf("e. Save and quit.\n");
printf(" Please enter an option from the main menu: ");
scanf("%c",&menu_option);
switch(menu_option){
case 'a':
//Learn_to_use();
break;
case 'b':
initials=get_intials();
printf( "input initials:%c\n", initials) ;
break;
case'c':
printf("case c");
//difficulty = get_difficulty();
break;
case'd':
break;
case'e':
break;
default:
printf("invalid input");
break;
}
}while(menu_option !='e');
}
output:
Please enter an option from the main menu: b
Please Enter Initials: c
input initials:c
/*
This code includes a stray \n from previous input due to which get_initials method was not working properly,it picked up the remanant \n in the input stream and concluded,
flushing the input stream is the solution to the problem, uncomment the code at line 8 to get proper functionality
*/
#include <stdio.h>
char get_intials(void){
char initails;
//fflush(stdin);
printf("Please Enter Initials: ");
scanf("%c",&initails);
return initails;
}
int main (void)
{
char menu_option,initials;
int difficulty;
printf(" EDUCATIONAL MATH PROGRAM!!!\n");
printf("------------------------------------------\n\n");
do{
printf("Main Menu\n");
printf("a. Learn about how to use program.\n");
printf("b. Enter your initials (3 individual letters).\n");
printf("c. Difficulty Selection.\n");
printf("d. Start a new sequence of problems.\n");
printf("e. Save and quit.\n");
printf(" Please enter an option from the main menu: ");
fflush(stdin);
scanf("%c",&menu_option);
switch(menu_option){
case 'a':
//Learn_to_use();
break;
case 'b':
initials=get_intials();
if(initials == '\n')
printf("\n%s\n","I was there in stream as newline");
//printf("\n%c",initials);
break;
case'c':
printf("case c");
//difficulty = get_difficulty();
break;
case'd':
break;
case'e':
break;
default:
printf("invalid input");
break;
}
}while(menu_option !='e');
return 0;
}
I'm trying to implement phonebook in C using data structure.
I found some source code and I'm trying to understand this code but there is really big problem I've never seen. It is dll. I googled about dll but there is nothing related about this. I know the meaning and purpose of dll, but why do we use fopen contact.dll ?
#include<stdio.h>
#include<conio.h>
#include<string.h>
#include<process.h>
#include<stdlib.h>
#include<dos.h>
struct contact
{
long phone;
char name[20],add[20],email[30];
} list;
char query[20],name[20];
FILE *fp, *ft;
int i,n,ch,l,found;
int main()
{
main:
system("cls"); /* ************Main menu *********************** */
printf("\n\t **** Welcome to Contact Management System ****");
printf("\n\n\n\t\t\tMAIN MENU\n\t\t=====================\n\t\t[1] Add a new Contact\n\t\t[2] List all Contacts\n\t\t[3] Search for contact\n\t\t[4] Edit a Contact\n\t\t[5] Delete a Contact\n\t\t[0] Exit\n\t\t=====================\n\t\t");
printf("Enter the choice:");
scanf("%d",&ch);
switch(ch)
{
case 0:
printf("\n\n\t\tAre you sure you want to exit?");
break;
/* *********************Add new contacts************ */
case 1:
system("cls");
fp=fopen("contact.dll","a");
for (;;)
{
fflush(stdin);
printf("To exit enter blank space in the name input\nName (Use identical):");
scanf("%[^\n]",&list.name);
if(stricmp(list.name,"")==0 || stricmp(list.name," ")==0)
break;
fflush(stdin);
printf("phone:");
scanf("%ld",&list.phone);
fflush(stdin);
printf("address:");
scanf("%[^\n]",&list.add);
fflush(stdin);
printf("email address:");
gets(list.email);
printf("\n");
fwrite(&list,sizeof(list),1,fp);
}
fclose(fp);
break;
/* *********************list of contacts************************* */
case 2:
system("cls");
printf("\n\t\t================================\n\t\t\tLIST OF CONTACTS\n\t\t================================\n\nName\t\tphone No\t Address\t\tE-mail ad.\n=================================================================\n\n");
for(i=97; i<=122; i=i+1)
{
fp=fopen("contact.dll","r");
fflush(stdin);
found=0;
while(fread(&list,sizeof(list),1,fp)==1)
{
if(list.name[0]==i || list.name[0]==i-32)
{
printf("\nName\t: %s\nphone\t: %ld\nAddress\t: %s\nEmail\t: %s\n",list.name,
list.phone,list.add,list.email);
found++;
}
}
if(found!=0)
{
printf("=========================================================== [%c]-(%d)\n\n",i-32,found);
getch();
}
fclose(fp);
}
break;
/* *******************search contacts********************** */
case 3:
system("cls");
do
{
found=0;
printf("\n\n\t..::CONTACT SEARCH\n\t===========================\n\t..::Name of contact to search: ");
fflush(stdin);
scanf("%[^\n]",&query);
l=strlen(query);
fp=fopen("contact.dll","r");
system("cls");
printf("\n\n..::Search result for '%s' \n===================================================\n",query);
while(fread(&list,sizeof(list),1,fp)==1)
{
for(i=0; i<=l; i++)
name[i]=list.name[i];
name[l]='\0';
if(stricmp(name,query)==0)
{
printf("\n..::Name\t: %s\n..::phone\t: %ld\n..::Address\t: %s\n..::Email\t: %s\n",list.name,list.phone,list.add,list.email);
found++;
if (found%4==0)
{
printf("..::Press any key to continue...");
getch();
}
}
}
if(found==0)
printf("\n..::No match found!");
else
printf("\n..::%d match(s) found!",found);
fclose(fp);
printf("\n ..::Try again?\n\n\t[1] Yes\t\t[0] No\n\t");
scanf("%d",&ch);
}
while(ch==1);
break;
/* *********************edit contacts************************/
case 4:
system("cls");
fp=fopen("contact.dll","r");
ft=fopen("temp.dat","w");
fflush(stdin);
printf("..::Edit contact\n===============================\n\n\t..::Enter the name of contact to edit:");
scanf("%[^\n]",name);
while(fread(&list,sizeof(list),1,fp)==1)
{
if(stricmp(name,list.name)!=0)
fwrite(&list,sizeof(list),1,ft);
}
fflush(stdin);
printf("\n\n..::Editing '%s'\n\n",name);
printf("..::Name(Use identical):");
scanf("%[^\n]",&list.name);
fflush(stdin);
printf("..::phone:");
scanf("%ld",&list.phone);
fflush(stdin);
printf("..::address:");
scanf("%[^\n]",&list.add);
fflush(stdin);
printf("..::email address:");
gets(list.email);
printf("\n");
fwrite(&list,sizeof(list),1,ft);
fclose(fp);
fclose(ft);
remove("contact.dll");
rename("temp.dat","contact.dll");
break;
/* ********************delete contacts**********************/
case 5:
system("cls");
fflush(stdin);
printf("\n\n\t..::DELETE A CONTACT\n\t===============================\n\t..::Enter the name of contact to delete:");
scanf("%[^\n]",&name);
fp=fopen("contact.dll","r");
ft=fopen("temp.dat","w");
while(fread(&list,sizeof(list),1,fp)!=0)
if (stricmp(name,list.name)!=0)
fwrite(&list,sizeof(list),1,ft);
fclose(fp);
fclose(ft);
remove("contact.dll");
rename("temp.dat","contact.dll");
break;
default:
printf("Invalid choice");
break;
}
printf("\n\n\n..::Enter the Choice:\n\n\t[1] Main Menu\t\t[0] Exit\n");
scanf("%d",&ch);
switch (ch)
{
case 1:
goto main;
case 0:
break;
default:
printf("Invalid choice");
break;
}
return 0;
}
Judging by the way the file is used, contact.dll is not an actual Windows DLL, but a datafile that this application used to store phonebook entries.
The various cases add, remove, update, and retrieve list entries from the file. The name given to the file is misleading.
#include <stdio.h>
#include <stdlib.h> //for the clear screen function
#include <string.h>
struct customer
{
int custID;
char custName[50];
char custAddress[100];
};
typedef struct customer c;
void load_menu(void);
void customers_menu(void);
void createNew(void); //initialize your file
void add_Customer(c c1[30]); //add a new record to the file
FILE *fp;
int main(void)
{
load_menu();
return 0;
}
void load_menu(void)
{
int choice;
do
{
printf("Customer Orders Main Menu. \n\n");
printf("Please enter your choice: \n");
printf("1. Customer's Menu \n");
printf("2. Orders Menu\n");
printf("3. Product Stock Menu\n");
printf("4. Exit\n");
printf("\n");
if (scanf("%d",&choice)==1)
{
switch(choice)
{
case 1: system ("cls");
customers_menu();
printf("\n");
break;
case 2: system ("cls");
orders_menu();
printf("\n");
break;
case 3: system ("cls");
stock_menu();
printf("\n");
break;
case 4: printf("Quitting program!\n");
break;
default: printf("Invalid choice! Please try again\n");
printf("\n");
break;
}
}
else
{
fflush(stdin);
printf("Characters are invalid, please enter a number: \n ");
choice=0;
}
}while((choice !=4));
}
void createNew(void)
{
FILE *fp;
fp=fopen("Customer.dat", "w");
if (fp==NULL)
printf("File creation failed! \n");
else
{
printf("File created! \n");
fclose(fp);
}
}
void add_Customer (c c1[30])
{
int i, n , cc=0;
FILE *fp;
fp=fopen("Customer.dat", "a");
system("cls");
if(fp==NULL)
{
printf("File Creation Failed!");
}
system("cls");
printf("Enter the number of Customers: ");
scanf("%d", &n);
for(i=0;i<n;i++)
{
printf("Customer's ID (numbers only) : ");
scanf("%d", &c1[i].custID);
printf("Customer's Name : ");
gets(c1[i].custName);
printf("Customer's Address : ");
gets(c1[i].custAddress);
fwrite(&c1[i], sizeof(c), 1, fp);
}cc++;
fclose(fp);
}
void recordCount(c c1[30], int *count)
{
add_Customer(c1);
count=0;
count++;
}
void customers_menu(void)
{
int choice;
c c1[30];
int i;
do
{
printf("\n");
printf("Customers Menu \n\n");
printf("Please enter your choice: \n");
printf("1. Add Customer \n");
printf("2.\n");
printf("3.\n");
printf("4. Go back to Main Menu \n");
recordCount (c1, &i);
if (scanf("%d",&choice)==1)
{
switch(choice)
{
case 1: add_Customer(c1);
createNew();
printf("\n");
break;
case 2:
printf("\n");
break;
case 3:
printf("\n");
break;
case 4: printf("Going back to Main Menu\n");
system ("cls");
break;
default: printf("Invalid choice! Please try again\n");
printf("\n");
break;
}
}
else
{
fflush(stdin);
printf("Characters are invalid, please enter a number: \n ");
choice=0;
}
}while((choice !=4));
I have a problem since when I enter the Customers Menu it is staring to execute case 1 immediately (which still doesn't work properly). Can someone help me fix this error please because I tried everything I know and it is still in vain
I think your issue is that in customers_menu() you output the menu, but do not read the selection, instead you call recordCount() which directly calls addCustomer().
After addCustomer() we return the customers_menu() which then calls scanf() for the long gone menu.
A few other notes:
gets() is not good, I suggest you use scanf() (with %s) instead.
Doing a printf() then clearing the screen is a bit pointless.
Error messages should really go to stderr (fprintf(stderr,...)) rather than stdout (printf(...))
You code is a missing trailing }.
cc is added to, but not used.
This problem coming from if (scanf("%d",&choice)==1) because scanf will not return choice. If you enter valid answer (like number), then it returns 1 and switch case work with 1. I think that's the problem.
If you enter char instead of integer, scanf will return 0.