I tried to make a program to add a string to a set of strings but the checking for existing string part didn't work. It just passes the do-while and add straight into the list.
void Add(char index[MAXN][24], int *pi)
{
char name[24];
int n, name_check;
do {
printf("Add a student : ");
fflush(stdin);
scanf("%23[^\n]", name);
name_check = 1;
for (n = 0; n < *pi; n++)
if (strcmp(name,index[n]) == 0)
{
printf("Existing name found.\n");
name_check = 0;
n = *pi - 1;
}
} while (!name_check);
strcpy(index[*pi], Trim(name));
(*pi)++;
printf("Added.\n");
}
your problems comes from that line :
scanf("%23[^\n]", name);
you read the name up to the newline, the newline is not read, and because fflush(stdin); does nothing the newline is still available, so after you read one name in the very first call of Add the next times the input contains just the newline and nothing is read, so you use name not initialized with an undefined behavior
replace the line by
scanf(" %23[^\n]", name);
doing that you bypass the possible newline and also the other spaces starting the input, that also have the great advantage to not limit the length of the read name to 13 in case the input start by 9 spaces
doing the minimum, so removing the useless fflush and modifying the format of the scanf and adding a Trim doing nothing :
#include <stdio.h>
#include <string.h>
char * Trim(char *s)
{
return s;
}
#define MAXN 10
void Add(char index[MAXN][24], int *pi)
{
char name[24];
int n, name_check;
do {
printf("Add a student : ");
scanf(" %23s", name);
name_check = 1;
for (n = 0; n < *pi; n++)
if (strcmp(name,index[n]) == 0)
{
printf("Existing name found.\n");
name_check = 0;
break;
}
} while (!name_check);
strcpy(index[*pi], Trim(name));
(*pi)++;
printf("Added.\n");
}
int main()
{
char index[MAXN][24];
int p = 0;
int i;
Add(index, &p);
Add(index, &p);
for (i = 0; i != p; ++i)
puts(index[i]);
return 0;
}
Compilation and execution:
/tmp % gcc -Wall d.c
/tmp % ./a.out
Add a student : aze
Added.
Add a student : aze
Existing name found.
Add a student : qsd
Added.
aze
qsd
/tmp %
I encourage you to always check the value of scanf, if you did you was able to detect it returns 0 except the very first time and you found your error.
an other problem occurs, the spaces at the end of the name are not removed by scanf, immediately after you read the name you need to trim it then to compare it with the memorized names. In your code if we forget the newline not flush and you enter "aze" then "aze " etc you will save two times "aze" (of course all inputs without the '"')
Out of that your program can be simplified, for instance you do not need name because you can read in index[*pi] directely and save the strcpy, name_check is also useless because you can check the value of n after the loop or move the end of the function into the loop then return etc.
Related
I am trying to work on a employee management system that takes employee information as input and prints the output accordingly.
Structure:
struct employee
{
char empId[10];
char name[20];
char empType[10];
int dd, mm, yyyy;
};
Program to check if the string contains only integers:
void checkValidId(char *id)
{
int count = 0, i;
for(i = 0; i < strlen(id); i++)
{
if(id[i] >= '0' && id[i] <= '9')
{
count++;
}
}
if(count == strlen(id))
// continue executing next statements of input() function
else
// take the empId input again
}
Function to take input:
struct employee input()
{
struct employee e;
printf("Enter Employee ID: ");
scanf("%s", &e.empId);
checkValidId(e.empId);
// next statements ....
}
Here I am trying to check if the string input that is empId contains only integers which is done by checkValidId(). If yes then the program continues executing next statements. Else I want to take the input empId again. How to do it.
Requesting help!
Thanks!
Include the header <ctype.h>, and use isdigit to test if a character is in the set '0' ... '9'.
Include the header <stdbool.h>, and change the signature of checkValidId to
bool checkValidId(const char *id)
in order to indicate a result to the calling function.
In checkValidId, loop through each character of the string. If the current character is not a digit, immediately return false from the function. If the loop finishes, all the characters must be digits, so you can then return true.
Note that there is no reason to call strlen here. Simply loop until the current character is the null-terminating byte.
&e.empId is of type char (*)[10], that is a pointer-to-array-of-10-char. The scanf specifier "%s" expects the type char *, or pointer-to-char. An array will decay to a pointer to its first element when passed to a function, so the the 'correct' way to call scanf here is scanf("%s", e.empId);.
That said, you must check that the return value of scanf is the expected number of conversions, otherwise you will be operating on indeterminate data.
Additionally, an unbound "%s" is as dangerous as the gets function, as it does not know when to stop reading data, and will easily overflow the provided buffer. You must provide a maximum field width to prevent scanf from reading too many characters. This should be at most the size of your buffer minus 1, leaving room for the null-terminating byte.
An example of using scanf safely:
if (1 != scanf("%9s", e.empId)) {
/* handle input stream error */
}
Note that when scanf fails to perform a conversion, the problem data is left in the stream. Recovering from bad input with scanf is very hard, and for that reason a line-based approach to user input is generally advised. This can be accomplished with fgets.
If there is room in the buffer, fgets includes the newline character when read. See Removing trailing newline character from fgets() input for an example usage of strcspn, which can also be used as a way to get the length of the input.
To repeatedly ask the user for input, use an infinite loop. Only break from the loop when the user correctly enters the requested data, or a critical error occurs.
Here is an example program, using the methods discussed:
#include <ctype.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
struct employee {
char empId[10];
/* ... */
};
bool checkValidId(const char *id)
{
for (size_t i = 0; id[i] != '\0'; i++)
if (!isdigit((unsigned char) id[i]))
return false;
return true;
}
bool getEmployee(struct employee *e, FILE *stream)
{
char buffer[256];
while (1) {
printf("Enter employee ID: ");
if (!fgets(buffer, sizeof buffer, stream))
return false;
size_t length = strcspn(buffer, "\r\n");
/* remove the newline */
buffer[length] = '\0';
if (!length)
fprintf(stderr, "Invalid ID. Zero length.\n");
else if (length >= sizeof e->empId)
fprintf(stderr, "Invalid ID. Too long.\n");
else if (!checkValidId(buffer))
fprintf(stderr, "Invalid ID. Contains non-digit character(s).\n");
else {
strcpy(e->empId, buffer);
break;
}
puts("Try again.");
}
return true;
}
int main(void)
{
struct employee emp;
if (!getEmployee(&emp, stdin))
return 1;
printf("ID: <%s>\n", emp.empId);
}
Interacting with this program:
Enter employee ID: foobar
Invalid ID. Contains non-digit character(s).
Try again.
Enter employee ID:
Invalid ID. Zero length.
Try again.
Enter employee ID: 1234567890
Invalid ID. Too long.
Try again.
Enter employee ID: 42
ID: <42>
checkValidId should return int so it can tell the caller whether the id is valid [or not].
A caller (e.g. input) should loop if the return value of checkValidId indicates a bad id.
No need to use strlen at all.
No need to compare lengths. A simpler algorithm can be used.
We can just stop the loop if an invalid char is detected
Here is the refactored code:
struct employee {
char empId[10];
char name[20];
char empType[10];
int dd, mm, yyyy;
};
// Program to check if the string contains only integers:
// RETURNS: 1=input valid, 0=retry
int
checkValidId(char *id)
{
int valid = 0;
for (int i = 0; id[i] != 0; i++) {
valid = (id[i] >= '0') && (id[i] <= '9');
if (! valid)
break;
}
return valid;
}
// Function to take input:
struct employee
input(void)
{
struct employee e;
while (1) {
printf("Enter Employee ID: ");
scanf("%s", &e.empId);
if (checkValidId(e.empId))
break;
}
// next statements ....
}
I am making a typedef to a structure for a "person" The person has a name, ssn and yearOfBirth. I am getting errors I do not understand with my for loops.
[Error] cannot convert 'person_t' to 'person_t*' for argument '1' to
'void getOnePerson(person_t*)'
This is the first file:
#include <stdio.h>
#include <string.h>
#include "structures.h"
void getOnePerson(person_t *p)
{
printf("Enter full name: ");
scanf("%99[^\n]", p -> name);
printf("Enter ssn: ");
scanf("%99[^\n]", p -> ssn);
printf("Enter year of birth: ");
scanf("%d", &p -> yearOfBirth);
}
void printOnePerson(person_t p)
{
printf("%s:", p.name);
printf("%s:", p.ssn);
printf("%s\n", p.yearOfBirth);
}
void getPeople(person_t p[], int numOfPeople)
{
for(int i = 0; i < sizeof(p); i++)
{
getOnePerson(p[i]);
}
}
void printPeople(person_t p[], int numOfPeople)
{
for(int i = 0; i < sizeof(p); i++)
{
printOnePerson(p[i]);
}
}
This is my structure file:
#define NAME_SIZE 80
#define SSN_SIZE 13
#define NUM_PEOPLE 10
typedef struct
{
char name[NAME_SIZE];
char ssn[SSN_SIZE];
int yearOfBirth;
} person_t;
First of all, it seems to be pointers and references task. You may need to read this to understand them. In other words, cannot convert person_t to person_t* means you are trying to use your object person instead of reference to that specific person. * means reference, so you need to pass an address to it using &. Im not best explainer, check out the link instead and all answers, not only accepted one.
Code seems quite messy, I tried to fix it to compilable code, although I dont have C compiler (you may need to edit/fix according to your homework details):
#include <stdio.h>
#include <string.h>
#define NAME_SIZE 80
#define SSN_SIZE 13
#define NUM_PEOPLE 10
typedef struct
{
char name[NAME_SIZE];
char ssn[SSN_SIZE];
int yearOfBirth;
} person_t;
int main()
{
person_t people[NUM_PEOPLE];
printf("Get people\n");
getPeople(&people, 3);
printf("\nPrint people\n");
printPeople(people, 3);
return 0;
}
void getOnePerson(person_t *person)
{
printf("Enter full name: ");
scanf("%s", person -> name);
printf("\nEnter ssn: ");
scanf("%s", person -> ssn);
printf("\nEnter year of birth: ");
scanf("%s", person -> yearOfBirth);
}
void printOnePerson(person_t p)
{
printf("%s:%s:%d\n", p.name, p.ssn, p.yearOfBirth);
}
void getPeople(person_t *person[], int num)
{
int i;
for(i=0; i<num; i++)
{
getOnePerson(&person[i]);
}
}
void printPeople(person_t person[], int num)
{
int i;
for(i=0; i<num; i++)
{
printOnePerson(person[i]);
}
}
So, briefly, your getPeople(person_t *person[], int num) function's first parameter is person_t *person[], therefore you need to pass a &people. Same as getOnePerson(person_t *person) parameter person_t *person means you need to pass address to a single person object &person[i]. The meaning behind them that using references, you can edit the values in these objects directly in the function. While printPeople(person_t person[], int num) and printOnePerson(person_t p) are used for reading (not editing) thereby you can pass values themselves.
You have such a large number of small problems, it is difficult to know where to begin. First a nit, you never include spaces around "->" when referencing a structure member. Use p->name, not p -> name. Continuing...
You fail to validate the return of scanf. You must check the return Every Time, or you are tempting Undefined Behavior. You also must change "%99[^\n]" to " %79[^\n]" because neither "%c" or "%[...]" consume leading whitespace. Failing to add the " " before %12[^\n] would make it impossible to read p->ssn and lead to a matching failure reading p->yearOfBirth.
Note the change from 99 to 79. You #define NAME_SIZE 80 and declare char name[NAME_SIZE];, what do you think you are doing using a field-width modifier of 99 when at most 79 characters can be stored in name? (You have the same problem with #define SSN_SIZE 13). You use the field-width modifier with scanf to protect your array bounds. Setting the *field-width modifier greater than your array size (-1) removes the protection it should provide altogether.
Your failure to check the return of scanf and handle the three cases of return necessary will lead to Undefined Behavior if the user accidentally makes a single error in input. Failure to check the return of scanf is one of the most common pitfall new C programmer fall into. It is mandatory for every user input. Otherwise, you can have no confidence your code is actually processing valid data.
scanf can be used, if used correctly. This means you are responsible for checking the return of scanf every time. You must handle three conditions
(return == EOF) the user canceled input by generating a manual EOF by pressing Ctrl+d (or on windows Ctrl+z, but see CTRL+Z does not generate EOF in Windows 10 (early versions));
(return < expected No. of conversions) a matching or input failure occurred. For a matching failure you must account for every character left in your input buffer. (scan forward in the input buffer reading and discarding characters until a '\n' or EOF is found); and finally
(return == expected No. of conversions) indicating a successful read -- it is then up to you to check whether the input meets any additional criteria (e.g. positive integer, positive floating-point, within a needed range, etc..).
A short function implementation to empty all remaining characters in stdin in the event of matching failure could be as simple as:
void empty_stdin (void)
{
int c = getchar();
while (c != '\n' && c != EOF)
c = getchar();
}
(implementing in your code is left as an exercise for you)
Further, using type void as the return of an input function makes no sense. You must choose your return to provide the return of required information AND provide an indication of whether the input succeeded or failed. Using void for getOnePerson() means you have no way of knowing whether you received all valid input, or just received name, but not ssn, or if the user simply generated a manual EOF canceling input at each prompt. A simple integer return is all you need (e.g. return 0; on failure or return 1; only after all 3-inputs are validated) You could do something like:
int getOnePerson (person_t *p)
{
int rtn; /* scanf return */
/* validate each input for all 3 cases */
fputs ("\nEnter full name: ", stdout); /* no need for printf, no conversion */
if ((rtn = scanf (" %79[^\n]", p->name)) != 1) {
if (rtn == EOF)
puts ("(input complete)");
else
fputs ("error: invalid format 'p->name'.\n", stderr);
return 0;
}
/* validate each input for all 3 cases */
fputs ("Enter ssn: ", stdout); /* ditto */
if ((rtn = scanf (" %12[^\n]", p->ssn)) != 1) { /* " */
if (rtn != EOF)
fputs ("error: invalid format 'p->ssn'.\n", stderr);
return 0;
}
/* validate each input for all 3 cases */
fputs ("Enter year of birth: ", stdout);
if ((rtn = scanf ("%d", &p->yearOfBirth)) != 1) {
if (rtn != EOF)
fputs ("error: invalid format 'p->yearOfBirth'.\n", stderr);
return 0;
}
return 1; /* indicates all 3 input successfully received */
}
(note: input is complete when EOF is encountered, either manually generated by the user or encountered in the input stream)
void is also meaningless as a return for getPeople(). You can't use a for loop and just assume all inputs were successful, instead, you need to take input only while input is available, while protecting your array bounds, and then return the number of input actually received (which may be less than NUM_PEOPLE). Further, choose your type properly. For counters, size_t is the proper type (you can't have a negative number of persons), e.g.
size_t getPeople (person_t *p, size_t numOfPeople)
{
// for(int i = 0; i < sizeof(p); i++)
// {
// getOnePerson(p[i]);
// }
size_t n = 0;
while (n < numOfPeople && getOnePerson (&p[n]))
n++;
return n;
}
When you pass an array as a parameter to a function, the array is converted to a pointer to the first element. So when you do sizeof(p) within a function -- that is not what you want and does not provide the number of elements in the array referenced by p -- what it does provide is sizeof(a_pointer), which is fixed by your compiler (e.g. 8-bytes on x86_64, 4-bytes on x86). You pass numOfPeople -- use it, e.g.
void printPeople (person_t *p, size_t numOfPeople)
{
puts ("\nStored People\n");
// for(int i = 0; i < sizeof(p); i++)
for (size_t i = 0; i < numOfPeople; i++)
{
printOnePerson(p[i]);
}
}
You will also want to fix printf("%s\n", p.yearOfBirth); (yearOfBirth is not a string...)
Your header is fine, but it is missing something. Always include header guards around the content of your header files to prevent multiple inclusions of the file, e.g.
#ifndef mystructures_h
#define mystructures_h 1
...
/* your header content */
...
#endif
(note: the 1 isn't required, but if you are defining a constant, it is never a bad idea to give it an affirmative value of your choosing)
There are probably more that were corrected, but those were the major points. Putting it altogether, you could do:
structures.h
#ifndef mystructures_h
#define mystructures_h 1
#include <stdio.h>
#define NAME_SIZE 80
#define SSN_SIZE 13
#define NUM_PEOPLE 10
typedef struct {
char name[NAME_SIZE];
char ssn[SSN_SIZE];
int yearOfBirth;
} person_t;
size_t getPeople (person_t *p, size_t numOfPeople);
void printPeople (person_t *p, size_t numOfPeople);
#endif
(can you figure out why #include <stdio.h> was moved from structures.c into structures.h? do you know why the function prototypes for getPeople() and printPeople() are required in the header and not the rest?)
structures.c
#include "structures.h"
int getOnePerson (person_t *p)
{
int rtn; /* scanf return */
fputs ("\nEnter full name: ", stdout);
if ((rtn = scanf (" %79[^\n]", p->name)) != 1) {
if (rtn == EOF)
puts ("(input complete)");
else
fputs ("error: invalid format 'p->name'.\n", stderr);
return 0;
}
fputs ("Enter ssn: ", stdout); /* ditto */
if ((rtn = scanf (" %12[^\n]", p->ssn)) != 1) { /* " */
if (rtn != EOF)
fputs ("error: invalid format 'p->ssn'.\n", stderr);
return 0;
}
fputs ("Enter year of birth: ", stdout);
if ((rtn = scanf ("%d", &p->yearOfBirth)) != 1) {
if (rtn != EOF)
fputs ("error: invalid format 'p->yearOfBirth'.\n", stderr);
return 0;
}
return 1;
}
size_t getPeople (person_t *p, size_t numOfPeople)
{
// for(int i = 0; i < sizeof(p); i++)
// {
// getOnePerson(p[i]);
// }
size_t n = 0;
while (n < numOfPeople && getOnePerson (&p[n]))
n++;
return n;
}
void printOnePerson (person_t p)
{
printf("%s:", p.name);
printf("%s:", p.ssn);
// printf("%s\n", p.yearOfBirth);
printf("%d\n", p.yearOfBirth);
}
void printPeople (person_t *p, size_t numOfPeople)
{
puts ("\nStored People\n");
// for(int i = 0; i < sizeof(p); i++)
for (size_t i = 0; i < numOfPeople; i++)
{
printOnePerson(p[i]);
}
}
A short test program peopletest.c
#include "structures.h"
int main (void) {
person_t people[NUM_PEOPLE] = {{ .name = "" }};
size_t npeople = getPeople (people, NUM_PEOPLE);
printPeople (people, npeople);
}
Example Use/Output
$ ./bin/peopletest
Enter full name: Person A. One
Enter ssn: 123456789
Enter year of birth: 2001
Enter full name: Person B. Two
Enter ssn: 234567890
Enter year of birth: 2002
Enter full name: Person C. Three
Enter ssn: 345678901
Enter year of birth: 2003
Enter full name: (input complete)
Stored People
Person A. One:123456789:2001
Person B. Two:234567890:2002
Person C. Three:345678901:2003
Look things over and let me know if you have further questions.
I was working on this sample exercise, and everything works as I would like it to, but there is one behavior I don't understand.
When providing input: if I make consecutive invalid entries everything seems to work great. But if I enter a number different from 1,2,3 in the case of the first question, or 1,2 in the case of the second question, the program just sits there until a new input is given. If another invalid entry is made, it goes back to the error "invalid entry" message, and if an appropriate number is entered, everything moves along fine.
I do not understand why it stops to wait for a second input...anyone?
Thanks guys.
#include <stdio.h>
static int getInt(const char *prompt)
{
int value;
printf("%s",prompt);
while (scanf("%d", &value) !=1)
{
printf("Your entry is invalid.\nGive it another try: %s", prompt);
getchar();
scanf("%d", &value);
}
return value;
}
int main() {
int wood_type, table_size, table_price;
printf("Please enter " );
wood_type = getInt("1 for Pine, 2 for Oak, and 3 for Mahogany: ");
printf("Please enter ");
table_size = getInt("1 for large, 2 for small: ");
printf("\n");
switch (wood_type) {
case 1:
table_price = (table_size == 1)? 135:100;
printf("The cost of for your new table is: $%i", table_price);
break;
case 2:
table_price = (table_size == 1)? 260:225;
printf("The cost of for your new table is: $%i", table_price);
break;
case 3:
table_price = (table_size == 1)? 345:310;
printf("The cost of for your new table is: $%i", table_price);
break;
default:
table_price = 0;
printf("The cost of for your new table is: $%i", table_price);
break;
}
}
You most likely need to flush your input buffer (especially with multiple scanf calls in a function). After scanf, a newline '\n' remains in the input buffer. fflush does NOT do this, so you need to do it manually. A simple do...while loop works. Give it a try:
edit:
static int getInt(const char *prompt)
{
int value;
int c;
while (printf (prompt) && scanf("%d", &value) != 1)
{
do { c = getchar(); } while ( c != '\n' && c != EOF ); // flush input
printf ("Invalid Entry, Try Again...");
}
return value;
}
The blank line you get if you enter nothing is the normal behavior of scanf. It is waiting for input (some input). If you want your routine to immediately prompt again in the case the [Enter] key is pressed, then you need to use another routine to read stdin like (getline or fgets). getline is preferred as it returns the number of characters read (which you can test). You can then use atoi (in <stdlib.h>) to convert the string value to an integer. This will give you the flexibility you need.
example:
int newgetInt (char *prompt)
{
char *line = NULL; /* pointer to use with getline () */
ssize_t read = 0; /* number of characters read */
size_t n = 0; /* numer of chars to read, 0 no limit */
static int num = 0; /* number result */
while (printf ("\n %s ", prompt) && (read = getline (&line, &n, stdin)) != -1)
{
if ((num = atoi (line)))
break;
else
printf ("Invalid Input, Try Again...\n");
}
return num;
}
If some invalid input is entered, it stays in the input buffer.
The invalid input must be extracted before the scanf function is completed.
A better method is to get the whole line of input then work on that line.
First, put that input line into a temporary array using fgets(),
then use sscanf() (safer than scanf because it guards against overflow).
#include <stdio.h>
int main(int argc, const char * argv[]) {
char tempbuff[50];
int result, d , value;
do
{
printf("Give me a number: ");
fgets( tempbuff, sizeof(tempbuff), stdin ); //gets string, puts it into tempbuff via stdin
result = sscanf(tempbuff, "%d", &value); //result of taking buffer scanning it into value
if (result < 1){ //scanf can return 0, # of matched conversions,
//(1 in this case), or EOF.
printf("You didn't type a number!\n");
}
}while (result < 1);
//some code
return 0;
}
Knowledge from: http://www.giannistsakiris.com/2008/02/07/scanf-and-why-you-should-avoid-using-it/
Practice.c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define ARR 32
int main(void){
int MEM=64;
char arr[ARR],*p=(char *)calloc(MEM,(sizeof(char))),*q=NULL;
int i=0,j=1;
printf("\nEnter String : ");
while(j){
scanf(" %[^\n]s " ,arr);
if(j==1)
strcpy(p,arr);
else
strcat(p,arr);
if((j*ARR)==MEM){
MEM=MEM+(j*ARR);
q=realloc(p, MEM);
if(!(q)){
printf("\nNOT ENOUGH MEMORY\n");
goto END;
}
p=q;
}
for(i=0;i<(strlen(arr));++i){
if(arr[i]=='\n')
break;
}
if(arr[i]=='\n')
break;
++j;
}
printf("\n %s\n",p);
END: free(p);p=NULL;q=NULL;
return 0;
}
I am trying to get multiple string inputs.
I am using scanf(" %[^\n]s",arr); to take the input instead of fgets(arr,ARR,stdin);, because with fgets the program execution stops as soon as I hit ENTER key. But with scanf(" %[^\n]s",arr); the program is unable to get out of the while() loop even after entering \n.
I would like to know the mistake or mistakes I have made while writing the code.
The canonical way of reading multiple lines of input in C is to use fgets in a loop, like
while (fgets(arr, sizeof(arr), stdin) != NULL)
{
if (arr_contains_special_input_to_exit_loop(arr))
break;
// Optionally check for and remove trailing newline from input
// Append `arr` to your data
}
The condition to exit the loop might be some special input or an empty line or something else completely.
One mistake is:
for(i=0;i<(strlen(arr));++i){
if(arr[i]=='\n')
break;
}
Looking earlier in you code you have:
scanf(" %[^\n]s " ,arr);
The [^\n] prevents any newlines \n from being contained in arr. So your loop that looks for (arr[i]=='\n') will never find any. Your next bit of code continues looking for non-existent newlines:
if(arr[i]=='\n')
break;
This last break also breaks out of your outer loop preventing you from asking for further input on finding a newline (which it shouldn't). Fix these issues and it should get much further allowing you to enter multiple items.
Edit:
With a bit of effort looking at what you were doing, I now have it taking multiple input and reallocating as necessary. The strings are all concatenated and printed at the end. It could still stand a bit of work, but this should give you a few hints:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define ARR 32
int main (void) {
int MEM = 64;
char arr[ARR], *p = (char *) calloc (MEM, (sizeof (char))), *q = NULL;
int i = 0, j = 1;
while (j) {
printf ("\nEnter String : ");
scanf (" %[^\n]s ", arr);
printf (" you entered (arr): %s\n", arr);
if (strcmp (arr, "q") == 0) {
printf ("\n 'q' entered, exiting.\n\n"); // provide for exit if `q` entered
break;
}
if (j == 1)
strcpy (p, arr);
else
strcat (p, arr);
if ((j * ARR) == MEM) {
MEM = MEM + (j * ARR);
q = realloc (p, MEM);
if (!q) {
printf ("\nNOT ENOUGH MEMORY\n");
goto END;
}
else
printf ("\nMemory Reallocation - succeeded.\n");
p = q;
}
++j;
}
printf (" %s\n", p);
END:
if (p) free (p); /* always test pointer before calling free */
p = NULL;
q = NULL;
return 0;
}
output:
./bin/me
Enter String : fishinsea
you entered (arr): fishinsea
Enter String : alligators
you entered (arr): alligators
Memory Reallocation - succeeded.
Enter String : really_big_mosters
you entered (arr): really_big_mosters
Enter String : SuperSnake_Prudhome
you entered (arr): SuperSnake_Prudhome
Memory Reallocation - succeeded.
Enter String : 8_puppies
you entered (arr): 8_puppies
Enter String : q
you entered (arr): q
'q' entered, exiting.
fishinseaalligatorsreally_big_mostersSuperSnake_Prudhome8_puppies
I created a program that asks the user to input their name, and then manipulates it in multiple ways. The final way that it manipulates it is by printing the users name backwards. For instance if the user entered John Doe, the program would print Doe John. The only problem I'm having at this point is stopping my program from putting an unnecessary new line between the last and first name.
Example:
I want Doe John on one line but I get
Doe
John
For my assignment I need to get rid of this extra line. How do I do this?
#include <stdio.h>
#include <string.h>
void removeNewLine (char * userName, int charLenght)
{
int i=0;
do {
if (userName [i]=='\n')
{
userName [i]='\0';
}
i++;
} while (i<charLenght);
}
// This is going to tell me exactly how many real character are in my array
int myCounter (char * userName, int size)
{
int counter=0;
do
{
if(userName [counter]=='\0')
{
return counter; //I always thought that you needed to put your return at the end of the function, this is good to know that you don't need too
}
counter++;
}while (counter<size);
return -1;
}
int main ()
{
printf("Enter your first and last name\n");
char name [250]={'\0'};
char * space;
char *first=NULL, *last = NULL, *firstspace;
char *userName;
int numOfChars=0;
//Prevents the potential problem of an overflow = (sizeof(name)-1)
fgets(name,(sizeof(name)-1),stdin);
//This is what is actually doing the dirty work of removing the extra chars
removeNewLine(userName, numOfChars);
//This is going to count the number of characters that were input by the user
numOfChars = strlen(name)-1;
printf("You Entered: %s \n", name);
printf("There are %zu characters in your name including the space. \n", strlen(name));
char end;
int i;
end = strlen(name) -1;
printf("Your name backwards is");
for (i = end; i >= 0; --i)
{
printf("%c", name [i]);
}
printf("\nLooking for the space in your name \n", name);
firstspace=space=strchr(name, ' ');
*firstspace='\0';
while (space!=NULL)
{
printf("The space was found at character %d\n", space-name+1);
last = space+1;
space=strchr(space+1, ' ');
}
printf("%s%s", last, name);
*firstspace=' ';
//This is just to tell the user how many "real" characters were in there name
printf("\n There are %d actual characters in your name including the space", numOfChars);
}
Do little modification and Interchange these below two lines
removeNewLine(userName, numOfChars);
//This is going to count the number of characters that were input by the user
numOfChars = strlen(name)-1;
Like this
numOfChars = strlen(name); // first find the length of input.
removeNewLine(name, numOfChars); // And now remove newline at the end of input
EDIT
Your CODE
#include <stdio.h>
#include <string.h>
void removeNewLine (char * userName, int charLenght)
{
int i=0;
do {
if (userName [i]=='\n')
{
userName [i]='\0';
}
i++;
} while (i<charLenght);
}
int main ()
{
printf("Enter your first and last name\n");
char name [250]={'\0'};
char * space;
char *first=NULL, *last = NULL, *firstspace;
int numOfChars=0;
//Prevents the potential problem of an overflow = (sizeof(name)-1)
fgets(name,(sizeof(name)-1),stdin);
//This is what is actually doing the dirty work of removing the extra chars
numOfChars = strlen(name); // first find the length of input.
removeNewLine(name, numOfChars); // And now remove newline at the end of input
printf("You Entered: %s \n", name);
printf("There are %zu characters in your name including the space. \n", strlen(name));
char end;
int i;
end = strlen(name) -1;
printf("Your name backwards is");
for (i = end; i >= 0; --i)
{
printf("%c", name [i]);
}
printf("\nLooking for the space in your name \n", name);
firstspace=space=strchr(name, ' ');
*firstspace='\0';
while (space!=NULL)
{
printf("The space was found at character %ld\n", space-name+1);
last = space+1;
space=strchr(space+1, ' ');
}
printf("%s %s", last, name);
*firstspace=' ';
//This is just to tell the user how many "real" characters were in there name
printf("\n There are %d actual characters in your name including the space", numOfChars);
}
Output
Enter your first and last name
John Doe
You Entered: John Doe
There are 8 characters in your name including the space.
Your name backwards iseoD nhoJ
Looking for the space in your name
The space was found at character 5
Doe John
There are 9 actual characters in your name including the space
The best way is to use fgets() with a couple of helper functions:
/*Removes remaining characters from keyboard input buffer until next newline*/
/*Returns 0 if OK, a negative value if EOF.*/
int fpurge(FILE *f)
{
int c;
while((c=fgetc(f))!=EOF && c!='\n')
{ }
return (c==EOF ? -1 : 0);
}
/*Find and remove newline from string*/
/* Returns a nonzero value if found, zero if not. */
int truncate_newline(char *str)
{
int bRet=0;
if(str!=NULL)
{
char *pNewline = strchr(str, '\n');
if(pNewLine!=NULL)
{
bRet = 1;
*pNewLine = '\0';
}
}
return bRet;
}
/*Remove newline from string or excess characters from input buffer,
where appropriate.*/
/* Returns 0 if buffer is full, a positive value if line is complete,
a negative value if EOF (implies buffer full). */
int fclean(char *str, FILE *f)
{
int ret = 1;
if(!truncate_newline(str))
ret = fpurge(f);
return ret;
}
It's used this way:
char buf[42];
fgets(buf, sizeof buf, stdin);
fclean(buf);
Now you have a NULL-terminated, newlineless buf, and nothing in the input buffer to corrupt your next fgets call.
Like to offer an "after accepted" solution.
void *removeNewLineAfter_fgets(char *s) {
if (s) {
size_t l = strlen(s);
if ((l > 0) && (s[l-1] == '\n')) {
s[l-1] = '\0';
}
}
return s;
}
// Usage:
if (removeNewLineAfter_fgets(fgets(name,sizeof(name),stdin)) == NULL) { handle EOF }
BTW: OP does not need -1 in fgets(name,(sizeof(name)-1),stdin).