This is a school assignment but I cannot get my loop to work. We have to use scanf and terminate the loop when an EOF is inputted. This is the part of the code that is the problem:
{int
main(void){
char str[MAX];
while(scanf("%s", str) != EOF)
{
printf("\nEnter a String: ");
scanf("%s", str);
two_ele_subs(str);
}
return 0;
}
The sscanf returns the number of read variables, that in your case is only one, or EOF (ie: -1) in case of end of file. So I suggest you to use a different approach, like in the following:
#include <stdio.h>
#define MAX 100
int main(void){
char str[MAX];
int retVal;
printf("\nEnter a String: ");
while((retVal = scanf("%s", str)) == 1 || retVal != EOF)
{
printf("\nEnter a String: ");
two_ele_subs(str);
}
return 0;
}
Related
I just started programming in C and I was wondering why I can't store a string with multiple words with scanf().
For example, I enter: "That's an example" and it's stores only the first word "That's"
My code:
int main(void) {
char string[100];
printf("Please enter something: ");
scanf("%s", &string);
printf("You entered: %s", string);
return (0);
}
You can let scanf() read more than one word with the character class conversion specifier: %[^\n] will stop at the newline and leave it pending in the input stream. Note that you must tell scanf the maximum number of characters to store into the destination array to avoid undefined behavior on long input lines. When passing an array to scanf(), you should not pass its address as &string, but just pass string as arrays decays into a pointer to their first element when passed as a function argument.
Here is a modified version:
#include <stdio.h>
int main(void) {
char string[100];
int c;
for (;;) {
printf("Please enter something: ");
/* initialize `string` in case the `scanf()` conversion fails on an empty line */
*string = '\0';
if (scanf("%99[^\n]", string) == EOF)
break;
printf("You entered: %s\n", string);
/* read the next byte (should be the newline) */
c = getchar();
if (c == EOF) /* end of file */
break;
if (c != '\n')
ungetc(c, stdin); /* not a newline: push it back */
}
return 0;
}
Note however that it is much simpler to use fgets() for this task:
#include <stdio.h>
int main(void) {
char string[100];
for (;;) {
printf("Please enter something: ");
if (!fgets(string, sizeof string, stdin))
break;
/* strip the trailing newline, if any */
string[strcspn(string, "\n")] = '\0';
printf("You entered: %s\n", string);
}
return 0;
}
#include <stdio.h>
#define BUFF_SIZE 512
int main(void) {
char string[BUFF_SIZE];
printf("Enter something: ");
fgets(string, BUFF_SIZE, stdin);
printf("You entered: %s", string);
return (0);
}
fgets() is the best option
I think there's a problem in you scanf(); I recommend you to remove & from it. then your code should see like that:
int main(void) {
char string[100];
printf("Please enter something: ");
scanf("%s", string);
printf("You entered: %s", string);
return (0);
}
In the c language, there is no data type called a string.
A string is stored as an array of characters.
Moreover, the variable itself points to the first element of the array. Therefore, there is no need to use the '&' operator to pass the address.
So, all you have to do is the following:
int main(void) {
char string[100];
printf("Please enter something: ");
scanf("%s", string);
printf("You entered: %s", string);
return (0);
}
Don't use '&' in scanf function.
int main()
{
char string[100];
printf("Please enter something: ");
scanf("%[^\n]%*c",string);
printf("You entered: %s", string);
return 0;
}
According to https://man7.org/linux/man-pages/man3/scanf.3.html, %s will ignore white-space characters. To capture spaces you would have to use %c with the additional size of the input argument, or use %[ format. Check if scanf will add \0 byte to the end or not.
How do I break out of this while loop if the user just presses enter without typing anything.
int main()
{
while(1){
int integer;
printf("enter integer:");
scanf("%d",&integer);
}
return 0;
}
You can't. scanf is a horrible function and should be avoided (in particular, you should never use it for user input).
The easiest way to get user input working is to make sure all input is through fgets (which reads a whole line). You can then analyze that line, convert it to a number (e.g. with strtol, strtod, sscanf, ...), or do whatever you want with it.
Here's an example:
#include <stdio.h>
#include <string.h>
int main(void) {
while (1) {
char buf[200];
int integer;
printf("enter integer: ");
fflush(stdout);
if (!fgets(buf, sizeof buf, stdin)) {
/* input error or end of file reached */
break;
}
buf[strcspn(buf, "\n")] = '\0'; /* remove trailing newline, if any */
if (buf[0] == '\0') {
/* empty line */
break;
}
sscanf(buf, "%d", &integer);
}
return 0;
}
According to me...
Take input as a string
IF inputString equals to lineBreak
THEN break
OTHERWISE convert it into integer
int main()
{
while(1)
{
int integer;
char input[1024];
printf("enter integer:");
fgets (input, sizeof (input), stdin);
if (strcmp (input, "\n") == 0)
break;
integer = atoi(input);
}
return 0;
}
It is possible,
Initialise the value of integer with something that is not allowed in input
For eg if the input takes positive integers ,I initialise integer with -1
int main()
{
while(1){
int integer=-1;
printf("enter integer:");
scanf("%d",&integer);
if(integer==-1)
break;
}
return 0;
}
I've made a user-defined function for reading input and replacing newline character '\n' with '\0' so when I use printf statement for printing the string it won't add newline at the end.
char xgets(char *line, int size, FILE *stdn)
{
//READS THE LINE
fgets(line, size, stdn);
//REMOVES NEWLINE CHARACTER '\n' AND ADDS '\0'
line[strcspn(line, "\n")] = '\0';
return line;
}
When I call xgets inside main() function it works properly, but when it is called in other user-defined function it does not wait for user-input.
I'm using Visual Studio 2015 for debugging my code.
Here's my code:
#include<stdio.h>
#include<stdlib.h>
#include<process.h>
//USER-DEFINED FUNCTION
char xgets(char *line, int size, FILE *stdn);
void sortm_hgrade();
void sortm_rcharge();
void header(void);
void header(void)
{
printf("*-*-*-*-*HOTEL_INFO*-*-*-*-*");
printf("\n\n");
}
char xgets(char *line, int size, FILE *stdn)
{
//READS THE LINE
fgets(line, size, stdn);
//REMOVES NEWLINE CHARACTER '\n' AND ADDS '\0' END LINE CHARACTER
line[strcspn(line, "\n")] = '\0';
return line;
}
#define MAX 1000
//PROGRAMS STARTS HERE
int main(void)
{
//VARIABLE-DECLARATION
int i = 0, j = 0, n = 0;
char line[MAX] = { 0 };
char o = { 0 };
char h[10] = { 0 };
//FUCNTION CALL-OUT
header();
printf("Type anything : ");
xgets(h, sizeof(h), stdin);
printf("Enter one option from the following : \n\n");
printf("(a) To Print out Hotels of a given Grade in order of charges. \n");
printf("(b) To Print out Hotels with Room Charges less than a given Value. \n");
printf("Please type a proper option. \n");
while (n == 0){
scanf_s(" %c", &o);
switch (o){
case 'a':
sortm_hgrade();
n = 1;
break;
case 'b':
sortm_rcharge();
n = 1;
break;
default:
printf("Option INVALID \n");
printf("Please type a proper option \n");
n = 0;
break;
}
}
//TERMINAL-PAUSE
system("pause");
}
void sortm_hgrade()
{
//FOR SORTING BY GRADE
char g[10] = { 0 };
printf("Enter the Grade : ");
xgets(g, sizeof(g), stdin);
printf("\n");
}
void sortm_rcharge()
{
printf("----");
}
You should change
scanf(" %c", &o);
to
scanf("%c ", &o);
This force scanf to consume trailing chars, like '\n'
In your code '\n' of user input for scanf %c is not consumed and it is consumed by fgets in your xgets function that exit immediately with an empty buffer.
BTW that solution can wok only if a single char is input by user.
Best code would be
char c;
while (n == 0)
{
o = getchar();
while ((c = getchar()) != EOF && c != '\n') ;
EDIT
With the second solution code is waiting, and discarding, chars until a '\n' is triggered or end of file. In your specific case (using stdin as console) EOF is not mandatory. It will be mandatory in case of input is being read from a "real file".
You need to skip the \n character after you take in a character. you can command scanf for that. fgets reads that newline character up first and then hence it terminates. use this
scanf(" %c *[^\n]", &o);
This should do the trick
I am learning file handling in C.I have this code but it is not accepting string as an input to write it to a file.Any help will be appreciated.
#include<stdio.h>
#include<string.h>
#include <stdlib.h>
int main(void)
{
FILE * fp1;
fp1 = fopen("abc.txt","a+");
if(fp1==NULL)
{printf("An error occurred");
}
printf("Delete file?\n");
int a,c;
char name [20];
int flag=1;
int ch=1;
while(flag!=0)
{
printf("Enter id input \n");
scanf("%d",&a);
fprintf(fp1,"\n%d\t",a);
printf("Enter Name");
gets(name);
fputs(name, fp1);
printf("Enter No \n");
scanf("%d",&c);
fprintf(fp1,"\t%d\t",c);
printf("Write more then press 0 else 1");
scanf("%d",&ch);
if(ch==1)
{
flag=0;
}
}
fclose(fp1);
}
On running this code the code does not take an input after Enter Name and directly skips to Enter No.I want the output to be in a tabular form.
Use a getchar() after entering id because the \n of 1st scanf stays in buffer.
printf("Enter id input \n");
scanf("%d",&a);
getchar();
When you enter a number for scanf("%d",&a);, you type in a number and press the Enter key. The scanf consumes the number and leaves the newline character ('\n') in the standard input stream (stdin). When the execution of the program reaches gets(name);, gets sees the newline character and consumes it, storing it in name.
Firstly, never use gets as it is dangerous as it doesn't prevent buffer overflows. Use fgets instead:
fgets(name, sizeof(name), stdin);
Secondly, you have to get rid of the newline character. You can do this by flushing the stdin. Or you can simply scan and discard the newline character just after reading the number from scanf by changing
scanf("%d",&a);
to
scanf("%d%*c",&a);
%*c scans and discards a character.
gets() is deprecated, don't use it. you can still use scanf()...
as for the tabulation...think it through.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(void)
{
FILE* fp1;
fp1 = fopen("abc.txt", "a+");
if (fp1 == NULL) {
printf("An error occurred");
}
int a, c;
char name [20];
int flag = 1;
int ch = 1;
while (flag != 0) {
printf("Enter id input:\n");
scanf("%d", &a);
fprintf(fp1, "%d\t", a);
printf("Enter Name:\n");
scanf("%s", name);
fprintf(fp1, "%s\t", name);
printf("Enter No:\n");
scanf("%d", &c);
fprintf(fp1, "%d\n", c);
printf("Again (0) or Exit(1) ?:\n");
scanf("%d", &ch);
if (ch == 1) {
flag = 0;
}
}
fclose(fp1);
return 0;
}
Trying to input more than a single string in my program's strings array, for that used :
scanf("%80[^\r\n]", strings[i]);
fgets(string[i], MAXLEN, stdin);
a custom made function was also used:
int getString(char s[]) {
char ch;
int i=0;
while( (ch = getchar()) != '\n' && ch != EOF ) {
s[i] = ch;
++i;
}
s[i] = '\0';
fflush(stdin);
return i;
}
but unable to get input with more than one string each including white spaces
function gets() used to work earlier for me but since it is deprecated no alternative can be found
This is where it was used :
int getString(char s[]) {
char ch;
int i=0;
while( (ch = getchar()) != '\n' && ch != EOF ) {
s[i] = ch;
++i;
}
s[i] = '\0';
fflush(stdin);
return i;
}
struct vechileData
{
char vechileType[MAXLEN];
int begin_month;
int end_month;
double price;
} data[5];
int main(int argc, char const *argv[])
{
printf("Input Vechile data: \n");
int i=0;
while(i < 5) {
printf("Input vechile Type : \n");
fgets(data[i].vechileType, MAXLEN, stdin);
printf("Input begin month : \n");
scanf("%d", &data[i].begin_month);
printf("Input end monhth : \n");
scanf("%d", &data[i].end_month);
printf("Input price : \n");
scanf("%lf", &data[i].price);
++i;
}
printf("Input Vechile Type to display information about the vechile : \n");
char vech[MAXLEN];
fgets(vech, MAXLEN, stdin);
i=0;
while(i < 5) {
if (strcmp(vech,data[i].vechileType) == 0)
{
printf("vechileType: %s\n", data[i].vechileType);
printf("Begin month: %d\n", data[i].begin_month);
printf("End month: %d\n", data[i].end_month);
printf("Price : %lf\n", data[i].price);
}
++i;
}
return 0;
}
It skips the next input to string statement during run time, "seems to"
Your problem is really not a gets() issue.
None of the scanf("%d", ...) and scanf("%lf", ...) consume the '\n' after the number and thus contribute to your issue. It is the next read of stdin to take in the '\n'. So when the next car type is read, it gets the lingering '\n'. Your 2nd car type ends up being "\n".
Use of fgets(data[i].vechileType, MAXLEN, stdin); puts a '\n' in data[i].vechileType. You likely do not want this. Your former use of gets() consumed, but did not put the '\n' in its return.
I long ago gave up doing user input with scanf() due to these subtle issues.
Recommend to separate input from parsing, use fgets() and then sscanf(). Example:
char number[80];
if (fgets(number, sizeof(number), stdin)) {
sscanf(number, "%d", &x)
Your implementation of a gets() replacement differs as follows
1) It does not return s (or NULL or error/eof).
2) It does not set eof indicator on eof.
3) Should getchar() return a '\0', your while loop errantly continues.
Recommend that if you must replace gets(), do so via fgets().
#define My_gets_N (1024 /* Some BA number */)
char *My_gets(char * str) {
char buffer[My_gets_N];
char *retval = fgets(buffer, sizeof(My_gets_N), stdin);
if (retval) {
int l = strlen(buffer);
/* fgets() saves '\n', but gets() does not */
if ((l > 0) && (buffer[l-1] == '\n')) {
l--;
}
memcpy(str, buffer, l);
str[l] = '\0';
return str;
}
else {
return 0;
}
}
If you replacement solution needs to deal with string length > the fixed My_gets_N, other coding is needed.
You must be more specific about what went wrong with the fgets() approach, that's the one I would recommend and it does work.
Note that fgets() will input the entire line, including linefeed/carriage returns at the end, so you might need to clean those off if they're undesirable to keep.
I don't understand how gets() worked for you, despite the warning that practically every C book post K&R gives, as it's not only deprecated, but extremely dangerous to use. Like the others have said, fgets() would definitely work if you used it correctly.
Instead of replacing all the instances of uses of gets with fgets. Use following Macros:
#define TRUNCATE_NULL(strText) \
{ \
int _strlen = strlen(strText); \
if (_strlen > 0 && strText[_strlen - 1] == '\n') strText[_strlen - 1] = '\0'; \
else while(fgetc(stdin)!='\n'); \
}
#define gets(strText) fgets(strText, sizeof(strText), stdin); TRUNCATE_NULL(strText);
Why use fgets?
Because it is more secure than gets.
Is gets really insecure?
Yes. It is greedy indeed, it will accept as much food as you give, even if it can not eat.
So technically, as #halfer rightly commented below,
with the use of gets, program is prone to buffer overflow.
How ?
char name[5];
gets(name);
Now provide input of more than 5 characters, it will accept it. This would overwrite data from memory, which should not be overwritten this way.
Ok with fgets, but why use TRUNCATE_NULL macro ?
fgets is not perfect either. it will accept \n (Enter) as character to be placed in input name.So to remove unnecessary \n, and to make sure expected functionality of gets is achieved we can use it.
Actually, there you can use while((getchar())!='\n'); to avoid such type of problem and one thing there is no need to use of fflush(stdin) function.
Here's code you can use
#include<stdio.h>
#include<string.h>
#define MAXLEN 50
int getString(char s[])
{
char ch;
int i=0;
while( (ch = getchar()) != '\n' && ch != EOF )
{
s[i] = ch;
++i;
}
s[i] = '\0';
return i;
}
struct vechileData
{
char vechileType[MAXLEN];
int begin_month;
int end_month;
double price;
}data[5];
int main(int argc, char const *argv[])
{
printf("Input Vechile data: \n");
int i=0;
while(i < 2)
{
printf("Input vechile Type : \n");
fgets(data[i].vechileType, MAXLEN, stdin);
printf("Input begin month : \n");
scanf("%d", &data[i].begin_month);
printf("Input end monhth : \n");
scanf("%d", &data[i].end_month);
printf("Input price : \n");
scanf("%lf", &data[i].price);
while((getchar())!='\n');
++i;
}
printf("Input Vechile Type to display information about the vechile : \n");
char vech[MAXLEN];
fgets(vech, MAXLEN, stdin);
i=0;
while(i < 2)
{
if (strcmp(vech,data[i].vechileType) == 0)
{
printf("vechileType: %s\n", data[i].vechileType);
printf("Begin month: %d\n", data[i].begin_month);
printf("End month: %d\n", data[i].end_month);
printf("Price : %lf\n", data[i].price);
}
++i;
}
return 0;
}
I hope this will help you.....