This question already has answers here:
Program doesn't wait for user input with scanf("%c",&yn);
(5 answers)
Closed 5 years ago.
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include "contacts.h"
int main(void)
{
int i = 0;
char middleInitial_ans;
// Declare variables here:
struct Name emp[] = { { 0 } };
struct Address addr[] = { { 0 } };
struct Numbers phone[] = { { 0 } };
// Display the title
puts("Contact Management System");
puts("-------------------------");
// Contact Name Input:
printf("Please enter the contact's first name: ");
scanf("%s", emp[i].firstName);
// PRINTING OUT FIRSTNAME
printf("%s\n\n", emp[i].firstName);
printf("Do you want to enter a middle intial(s)? (y or n): ");
scanf("%s", &middleInitial_ans); // Why doesn't the code work when I have %c instead of %s
printf("%c", middleInitial_ans);
if (middleInitial_ans == 'y') {
printf("Please enter the contact's middle initial(s): ");
scanf("%s", emp[i].middleInitial);
printf("\n%s\n", emp[i].middleInitial);
So at the end I am asking the user to input a character 'y' or 'n' to see if they want to enter in their middle initial. However when I use %c since they will be entering a single character the program entirely skips this code. When I use %s instead the program recognizes the code and works fine. I am wondering why that happens?
the '&' in C is basically pass by value, variable which has capability to store the address of the memory where value is stored.
you will need bigger memory for that. like an array or buffer.
%s expects the corresponding argument to be of type char *, and for scanf
char middleInitial_ans2[];
use this for %s
Related
This question already has answers here:
scanf() leaves the newline character in the buffer
(7 answers)
Closed 4 months ago.
So I was writing a quick program to get information about a patient from a hospital and it keeps skipping the scanf() at a certain point (at around line 34) and moves on to the scanf() after it. Here's the part that keeps bothering the life out of me:
#include<stdio.h>
#include<stdlib.h>
#include<windows.h>
int main(void){
char choice_1, choice_2, *blood_group, *spec_conditions, *allergies;
printf("Enter the patient's medical details.\n\n");
printf("Enter your blood group: ");
scanf("%s",&blood_group);
printf("Does the patient have any allergies:(y/n)");
scanf("%c",&choice_2);
if (choice_2 == 'y'){
printf("Kindly enter the allergies: ");
scanf("%s",&allergies);
}else{
allergies = "No allergies";
}
printf("\nDoes the patient have any special conditions:(y/n)");
scanf("%c",&choice_1);
if (choice_1 == 'y'){
printf("Kindly enter the condtion: ");
scanf("%s",&spec_conditions);
}else{
spec_conditions = "No special conditions";
}
printf("Displaying details...\n");
sleep(2);
system("cls");
printf("\t\t\tPATIENT DETAILS\n");
sleep(1);
return 0;
}
Problem 1:
char *blood_group, *spec_conditions, *allergies;
scanf("%s",&blood_group);
scanf("%s",&allergies);
scanf("%s",&spec_conditions);
What this does is it attempts to write a string of an unknown length to the address of char * variables, resulting in a 'buffer' overflow if the string is larger than a pointer, or a wild pointer that points to a random location.
Do not pass the address of the pointer to scanf, pass the pointer itself. Furthermore, the pointer must point to writable memory. This can be done by declaring it as an array.
Problem 2:
scanf("%c") reads the newline left when the user hits enter to read the string and moves on. Use scanf(" %c") instead to skip leading whitespace and read the actual character.
Try:
int main(void){
char choice_1, choice_2, blood_group[256], spec_conditions[256], allergies[256];
printf("Enter the patient's medical details.\n\n");
printf("Enter your blood group: ");
scanf("%255s",blood_group);
printf("Does the patient have any allergies:(y/n)");
scanf(" %c",&choice_2);
if (choice_2 == 'y'){
printf("Kindly enter the allergies: ");
scanf("%255s",allergies);
}else{
strcpy(allergies, "No allergies");
}
printf("\nDoes the patient have any special conditions:(y/n)");
scanf(" %c",&choice_1);
if (choice_1 == 'y'){
printf("Kindly enter the condtion: ");
scanf("%255s",spec_conditions);
}else{
strcpy(spec_conditions, "No special conditions");
}
printf("Displaying details...\n");
sleep(2);
system("cls");
printf("\t\t\tPATIENT DETAILS\n");
sleep(1);
return 0;
}
Hi I'm using to create a simple program that contains a list of Users (based on the struct below), and I'm trying to create new users based on user input, where I ask for each property seperately using scanf. But I'm having trouble with the structs limitations, for example id should be at max 10 chars and nome can have a max of 25 chars. Here's my code for more context:
struct user {
char id[10];
char name[25];
char group;
float score;
};
struct user list[25];
int registered = 0;
void createNewUser() {
struct user *userPtr, newUser;
userPtr = &newUser;
printf("\nId: ");
scanf("%10s", &(*userPtr).id);
printf("\nName: ");
scanf("%25s", &(*userPtr.name);
printf("\nGroup: ");
scanf("%c", &(*userPtr).group);
printf("\nScore: ");
scanf("%f", &(*userPtr).score);
insert(newUser);
printf("%10s\n", list[0].id);
printf("%25s\n", list[0].name);
printf("%c\n", list[0].group);
printf("%.1f\n", list[0].score);
}
void insert(struct user newUser) {
if (registered < 25){
list[registered] = newUser;
registered += 1;
}
}
With the code I presented above, if I type more than 10 chars for the first input, the next 2 are ignored. And my 3rd scanf is always ignored, the one for group. Can anyone here help me out with this?
The problem with scanf is that when it stops converting characters and there are
more in the input buffer (because the user entered more than you anticipated), then scanf will leave those characters there.
Specially the newline character (inputed when the user presses ENTER)
remains in the input buffer, which causes problems to subsequent calls of
scanf that read characters or strings. So in this case you have to "clean" the input buffer,
so that the next scanf does not consume the left overs of the previous scanf calls.
You can use this function after every scanf:
void clean_stdin(void)
{
int c;
while((c = getchar()) != '\n' && c != EOF);
}
Then you can do:
printf("\nId: ");
scanf("%10s", (*userPtr).id); // no need for &, id is char[]
clean_stdin();
printf("\nName: ");
scanf("%25s", (*userPtr).name); // same here
clean_stdin();
printf("\nGroup: ");
scanf("%c", &(*userPtr).group);
clean_stdin();
printf("\nScore: ");
scanf("%f", &(*userPtr).score);
Also note that the way you are if the maximal length of the ID is 10, then the
buffer must be of length 11, because in C you need to terminate the strings with
the '\0'-terminating byte. So change your structure to this:
struct user {
char id[11];
char name[26];
char group;
float score;
};
Also bear in mind, using a pointer like this
struct user *userPtr, newUser;
userPtr = &newUser;
printf("\nId: ");
scanf("%10s", (*userPtr).id);
...
is not necessary, it actually makes the code harder to read. You can do:
void createNewUser() {
struct user newUser;
printf("\nId: ");
scanf("%10s", newUser.id);
clean_stdin();
...
printf("\nScore: ");
scanf("%f", &newUser.score);
...
}
I am trying to have the user enter for the first, middle, and last name in my struct. The first scan works fine, any after that do not work. Here's my code so far
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include "contacts.h"
int main (void)
{
// Declare variables here:
struct Name names;
char yesNo;
// Display the title
printf("Contact Management System\n");
printf("-------------------------\n");
// Contact Name Input:
printf("Please enter the contact's first name: ");
scanf ("%d", &names.firstName);
printf("Do you want to enter a middle initial(s)? (y or n): ");
scanf(" %c", &yesNo);
while (yesNo == 'y' || yesNo == 'Y') {
printf("Please enter the contact's middle initial(s): ");
scanf(" %c%d", &names.middleInitial);
yesNo = 'n';
}
printf("Please enter the contact's last name: ");
scanf(" %c%d", &names.lastName);
Here's the struct in my header file
struct Name {
char firstName[31];
char middleInitial[7];
char lastName[36];
};
When I enter more than one character the program ends, when I enter just one character, the program skips the second scanf. I had the program working beforehand but I realized I needed to use structs so I switched from int's to the struct, and I haven't been able to make it work this way.
You are using scanf wrong.
scanf ("%d", &names.firstName);
names.firstName is a char array, but you are using %d which expects a
pointer to int, you are passing a pointer to an array. This is correct:
scanf("%30s", names.firstName);
Then you do
scanf(" %c%d", &names.middleInitial);
which has two errors: you are giving two conversion but passing only a on
pointer, and you are again passing the wrong pointer. Correct:
scanf("%6s", names.middleInitial);
and the same applies for scanf(" %c%d", &names.lastName);, the correct version
scanf("%35s", names.lastName);
In general, when using scanf with %s, you will have the problem that newline
and other strings are kept in the input buffer. This happens because %s
matches a sequence of non-white-space characters, so the newline (entered when
ENTER is pressed) will remain in the input buffer. Another example is
if the user enters two word separated by at least an empty space (like Hello Word),
%s would only read Hello. Subsequent calls of scanf may fail if they don't
anticipate this. That's why the best strategy is to clean the
buffer, use this function:
void clean_file_buffer(FILE *fp)
{
int c;
while((c = fgetc(fp)) != '\n' && c!=EOF);
}
And the you can use it like this:
printf("Please enter the contact's first name: ");
scanf ("%30s", names.firstName);
clean_file_buffer(stdin);
that takes care of left overs.
If you however want to have more control over the whole line, then you should
use fgets instead to read the whole line and then you can use sscanf to
parse it.
scanf("%s", names.firstName);
scanf(" %c", &yesNo);
scanf(" %s", names.middleInitial);
scanf(" %s", names.lastName);
or
scanf("%s", names.firstName);
getchar();
scanf("%c", &yesNo);
getchar();
scanf("%s", names.middleInitial);
getchar();
scanf("%s", names.lastName);
getchar();
and when yesNo question, if you typed over 1 character, first character will be into yesNo variable, and other chars will be into next input variable(names.middleInitial).
If you want to check the yesNo more carefully,
input yesNo as string. (but, buffer size check needed. buffer overflow.)
char yesNos[100];
scanf(" %s", &yesNos) ;
if ( yesNos[0]=='y' ) {...}
Yes ,I know that this question was already asked for many times ,but none of these helped me to discover the problem (duplicate...yeah). I want to read from input a series of strings into an array and then search from 'First Name'. If the name exist ,I want to display all the data stored in that element of array (I attached the code to undestand easily). When I run it ,I read from keyboard all the data ,but it returns me absolutely nothing.
#include<stdio.h>
typedef struct record {
char name[10],lname[10],phone[10],bday[10];
};
void main() {
struct record rec;
char search;
int i,nr;
printf("\nInput number of records: ");
scanf("%d",&nr);
for (i=0 ; i<nr ;i++) {
printf("First name: ");
scanf("%s",&rec.name[i]);
printf("Last name: ");
scanf("%s",&rec.lname[i]);
printf("Phone: ");
scanf("%s",&rec.phone[i]);
printf("Bday: ");
scanf("%s",&rec.bday[i]);
}
printf("Input the first name for searching: ");
scanf("%s",&search);
for (i=0 ;i<nr;i++) {
if (search == rec.name[i]) {
printf("First name: %s\nLast name: %s\nPhone: %s\nB-day: %s",rec.name[i],rec.lname[i],rec.phone[i],rec.bday[i]);
}
}
}
NOTE: I already replaced
scanf("%s",&rec.name[i]);
with
scanf("%s",rec.name[i]);
but no effect.
I believe there are a lot of problems with your code.
Firstly in this line:
scanf("%s",&search);
You have declared search as only a char, when really you want an array of chars. You also don't need & with search, as an array decays to a pointer to the first element.
It instead should be like this:
char search[10];
scanf("%9s", search); /* %9s to avoid buffer overflow */
You need to make this change to all your other scanf() calls, as this seems to be everywhere in this code.
It also seems that you want to create an array of records(structures), So you might need to make this after getting the value of nr. You can create it like this:
struct record rec[nr]; /* array of nr structures */
This also means calls like this:
rec.name[i]
Don't make sense, as you are iterating over the characters within a name, not over all the records in struct records.
This needs to be instead:
rec[i].name
Secondly, Your using == to compare strings, when you should be using strcmp instead. Using == will only compare the base address of the strings, not the actual contents of strings.
Your line should be this instead:
if (strcmp(search, rec[i].name) == 0) {
If you read the manual page for strcmp(), checking for a return value of 0 means that both strings are equal in comparison.
Lastly, in your first scanf() call:
scanf("%d",&nr);
You should really check the return value of this:
if (scanf("%d", &nr) != 1) {
/* exit program */
}
Note: For reading strings, you should really be using fgets instead. You can try upgrading to this later, but I think it is better to understand these basics first.
Here is working example of what your program should do:
#include <stdio.h>
#include <string.h>
#define STRSIZE 10
typedef struct {
char name[STRSIZE+1]; /* +1 to account for null-btye at the end */
char lname[STRSIZE+1];
char phone[STRSIZE+1];
char bday[STRSIZE+1];
} record;
int main() {
char search[STRSIZE+1];
int i,nr;
printf("\nInput number of records: ");
if (scanf("%d", &nr) != 1) {
printf("Invalid input.\n");
return 1;
}
record rec[nr]; /* array of records */
for (i = 0; i < nr ; i++) {
printf("First name: ");
scanf("%10s", rec[i].name);
printf("Last name: ");
scanf("%10s", rec[i].lname);
printf("Phone: ");
scanf("%10s", rec[i].phone);
printf("Bday: ");
scanf("%10s", rec[i].bday);
}
printf("Input the first name for searching: ");
scanf("%10s", search);
for (i = 0; i < nr; i++) {
if (strcmp(search, rec[i].name) == 0) {
printf("First name: %s\nLast name: %s\nPhone: %s\nB-day: %s\n",rec[i].name,rec[i].lname,rec[i].phone,rec[i].bday);
} else {
printf("Record not found.\n");
}
}
return 0;
}
The numeric input leaves a new line character in the input buffer, which is then picked up by the character input. when numeric input with scanf() skips leading white space, character input does not skip this leading white space.
Use a space before %c and it will help you cause if space is not used then a buffer added with value .so that use space before %c
scanf(" %c",&rec.name[i]);
This question already has answers here:
Why is getchar() reading '\n' after a printf statement?
(3 answers)
Closed 9 years ago.
This is a newbie question. I am new to C programming. I have the following code which does not prompt for 'Name' Onece the 'Age' is entered, it bypass the 'Name section.
#include <stdio.h>
int main()
{
char name[30],ch;
int age;
printf("Enter age : ");
scanf("%d", &age);
int i=0;
printf("Enter name: ");
while((ch = getchar())!='\n')
{
name[i]=ch;
i++;
}
name[i]='\0';
printf("Name: %s\n",name);
printf("Age : %d\n", age);
return 0;
}
After reading first prompt it bypass the second prompt which is using getchar() function. But if I change the order of prompt to ask for 'Name' first and then 'Age' it works fine.
The working code.
#include <stdio.h>
int main()
{
char name[30],ch;
int age;
int i=0;
printf("Enter name: ");
while((ch = getchar())!='\n')
{
name[i]=ch;
i++;
}
name[i]='\0';
printf("Enter age : ");
scanf("%d", &age);
printf("Name: %s\n",name);
printf("Age : %d\n", age);
return 0;
}
My coding IDE is CodeBlock and my compiler is GNU C Compiler (mingw32-gcc.exe)
Please help me to breakthrough.
A few improvements/advices to the code in the question:
the type of the return value of getchar() is int, so the type of ch also should be int
you could (and should, I believe) use format %s to read the name, this is easier and the leading white spaces in the input stream would not be a problem
the user of the code could give a name which contains more than 30 characters, and this input could crash your program, so you should protect your code for this possibility. You have two options:
a. use format '%29s" to read the name
b. change the definition of name to char *name, read it by scanf("%ms", &name);, and call free(name); after you do not need it anymore
Here is an example, in which the name can be very long and can include spaces:
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char *argv[])
{
char *name;
int age;
printf("Enter name: ");
scanf("%m[^\n]", &name);
printf("Enter age: ");
scanf("%d", &age);
printf("Name: %s\n", name);
printf("Age : %d\n", age);
free(name);
exit(EXIT_SUCCESS);
}
And here is a run of it:
$ ./a.out
Enter name: a very looooooooooooooooooooooooooooooooooooooooooooooong name
Enter age: 12
Name: a very looooooooooooooooooooooooooooooooooooooooooooooong name
Age : 12
In first code the \n character left behind by the scanf is read by getchar. This makes the condition (ch = getchar())!='\n' in while loop false and the loop body never get executed.
You need to consume that \n character which comes up to the buffer along with the age you entered on pressing Enter key.
Putting the statement
while(getchar()!='\n');
after the scanf will consume all of the newline characters.
Your second code is working fine because %d skips white-space characters unlike %c specifiers.