How can I split character and variable in 1 line?
Example
INPUT
car1900food2900ram800
OUTPUT
car 1900
food 2900
ram 800
Code
char namax[25];
int hargax;
scanf ("%s%s",&namax,&hargax);
printf ("%s %s",namax,hargax);
If I use code like that, I need double enter or space for make output. How can I split without that?
You should be able to use code like this to read one name and number:
if (scanf("%24[a-zA-Z]%d", namax, &hargax) == 2)
…got name and number OK…
else
…some sort of problem to be reported and handled…
You would need to wrap that in a loop of some sort in order to get three pairs of values. Note that using &namax as an argument to scanf() is technically wrong. The %s, %c and %[…] (scan set) notations all expect a char * argument, but you are passing a char (*)[25] which is quite different. A fortuitous coincidence means you usually get away with the abuse, but it is still not correct and omitting the & is easy (and correct).
You can find details about scan sets etc in the POSIX specification of scanf().
You should consider reading a whole line of input with fgets() or POSIX
getline(), and then processing the resulting string with sscanf(). This makes error reporting and error recovery easier. See also How to use sscanf() in loops.
Since you are asking this question which is actually easy, I presume you are somewhat a beginner in C programming. So instead of trying to split the input itself during the input which seems to be a bit too complicated for someone who's new to C programming, I would suggest something simpler(not efficient when you take memory into account).
Just accept the entire input as a String. Then check the string internally to check for digits and alphabets. I have used ASCII values of them to check. If you find an alphabet followed by a digit, print out the part of string from the last such occurrence till the current point. And while printing this do the same with just a slight tweak with the extracted sub-part, i.e, instead of checking for number followed by letter, check for letter followed by digit, and at that point print as many number of spaces as needed.
just so that you know:
ASCII value of digits (0-9) => 48 to 57
ASCII value of uppercase alphabet (A-Z) => 65 to 90
ASCII value of lowercase alphabets (a-z)
=> 97 to 122
Here is the code:
#include<stdio.h>
#include<string.h>
int main() {
char s[100];
int i, len, j, k = 0, x;
printf("\nenter the string:");
scanf("%s",s);
len = strlen(s);
for(i = 0; i < len; i++){
if(((int)s[i]>=48)&&((int)s[i]<=57)) {
if((((int)s[i+1]>=65)&&((int)s[i+1]<=90))||(((int)s[i+1]>=97)&&((int)s[i+1]<=122))||(i==len-1)) {
for(j = k; j < i+1; j++) {
if(((int)s[j]>=48)&&((int)s[j]<=57)) {
if((((int)s[j-1]>=65)&&((int)s[j-1]<=90))||(((int)s[j-1]>=97)&&((int)s[j-1]<=122))) {
printf("\t");
}
}
printf("%c",s[j]);
}
printf("\n");
k = i + 1;
}
}
}
return(0);
}
the output:
enter the string: car1900food2900ram800
car 1900
food 2900
ram 800
In addition to using a character class to include the characters to read as a string, you can also use the character class to exclude digits which would allow you to scan forward in the string until the next digit is found, taking all characters as your name and then reading the digits as an integer. You can then determine the number of characters consumed so far using the "%n" format specifier and use the resulting number of characters to offset your next read within the line, e.g.
char namax[MAXNM],
*p = buf;
int hargax,
off = 0;
while (sscanf (p, "%24[^0-9]%d%n", namax, &hargax, &off) == 2) {
printf ("%-24s %d\n", namax, hargax);
p += off;
}
Note how the sscanf format string will read up to 24 character that are not digits as namax and then the integer that follows as hargax storing the number of characters consumed in off which is then applied to the pointer p to advance within the buffer in preparation for your next parse with sscanf.
Putting it altogether in a short example, you could do:
#include <stdio.h>
#define MAXNM 25
#define MAXC 1024
int main (void) {
char buf[MAXC] = "";
while (fgets (buf, MAXC, stdin)) {
char namax[MAXNM],
*p = buf;
int hargax,
off = 0;
while (sscanf (p, "%24[^0-9]%d%n", namax, &hargax, &off) == 2) {
printf ("%-24s %d\n", namax, hargax);
p += off;
}
}
}
Example Use/Output
$ echo "car1900food2900ram800" | ./bin/fgetssscanf
car 1900
food 2900
ram 800
Related
I'm new to C and I'm trying to write a program that prints the ASCII value for every letter in a name that the user enters. I attempted to store the letters in an array and try to print each ASCII value and letter of the name separately but, for some reason, it only prints the value of the first letter.
For example, if I write "Anna" it just prints 65 and not the values for the other letters in the name. I think it has something to do with my sizeof(name)/sizeof(char) part of the for loop, because when I print it separately, it only prints out 1.
I can't figure out how to fix it:
#include <stdio.h>
int main(){
int e;
char name[] = "";
printf("Enter a name : \n");
scanf("%c",&name);
for(int i = 0; i < (sizeof(name)/sizeof(char)); i++){
e = name[i];
printf("The ASCII value of the letter %c is : %d \n",name[i],e);
}
int n = (sizeof(name)/sizeof(char));
printf("%d", n);
}
Here's a corrected, annotated version:
#include <stdio.h>
#include <string.h>
int main() {
int e;
char name[100] = ""; // Allow for up to 100 characters
printf("Enter a name : \n");
// scanf("%c", &name); // %c reads a single character
scanf("%99s", name); // Use %s to read a string! %99s to limit input size!
// for (int i = 0; i < (sizeof(name) / sizeof(char)); i++) { // sizeof(name) / sizeof(char) is a fixed value!
size_t len = strlen(name); // Use this library function to get string length
for (size_t i = 0; i < len; i++) { // Saves calculating each time!
e = name[i];
printf("The ASCII value of the letter %c is : %d \n", name[i], e);
}
printf("\n Name length = %zu\n", strlen(name)); // Given length!
int n = (sizeof(name) / sizeof(char)); // As noted above, this will be ...
printf("%d", n); // ... a fixed value (100, as it stands).
return 0; // ALWAYS return an integer from main!
}
But also read the comments given in your question!
This is a rather long answer, feel free to skip to the end for the code example.
First of all, by initialising a char array with unspecified length, you are making that array have length 1 (it only contains the empty string). The key issue here is that arrays in C are fixed size, so name will not grow larger.
Second, the format specifier %c causes scanf to only ever read one byte. This means that even if you had made a larger array, you would only be reading one byte to it anyway.
The parameter you're giving to scanf is erroneous, but accidentally works - you're passing a pointer to an array when it expects a pointer to char. It works because the pointer to the array points at the first element of the array. Luckily this is an easy fix, an array of a type can be passed to a function expecting a pointer to that type - it is said to "decay" to a pointer. So you could just pass name instead.
As a result of these two actions, you now have a situation where name is of length 1, and you have read exactly one byte into it. The next issue is sizeof(name)/sizeof(char) - this will always equal 1 in your program. sizeof char is defined to always equal 1, so using it as a divisor causes no effect, and we already know sizeof name is equal to 1. This means your for loop will only ever read one byte from the array. For the exact same reason n is equal to 1. This is not erroneous per se, it's just probably not what you expected.
The solution to this can be done in a couple of ways, but I'll show one. First of all, you don't want to initialize name as you do, because it always creates an array of size 1. Instead you want to manually specify a larger size for the array, for instance 100 bytes (of which the last one will be dedicated to the terminating null byte).
char name[100];
/* You might want to zero out the array too by eg. using memset. It's not
necessary in this case, but arrays are allowed to contain anything unless
and until you replace their contents.
Parameters are target, byte to fill it with, and amount of bytes to fill */
memset(name, 0, sizeof(name));
Second, you don't necessarily want to use scanf at all if you're reading just a byte string from standard input instead of a more complex formatted string. You could eg. use fgets to read an entire line from standard input, though that also includes the newline character, which we'll have to strip.
/* The parameters are target to write to, bytes to write, and file to read from.
fgets writes a null terminator automatically after the string, so we will
read at most sizeof(name) - 1 bytes.
*/
fgets(name, sizeof(name), stdin);
Now you've read the name to memory. But the size of name the array hasn't changed, so if you used the rest of the code as is you would get a lot of messages saying The ASCII value of the letter is : 0. To get the meaningful length of the string, we'll use strlen.
NOTE: strlen is generally unsafe to use on arbitrary strings that might not be properly null-terminated as it will keep reading until it finds a zero byte, but we only get a portable bounds-checked version strnlen_s in C11. In this case we also know that the string is null-terminated, because fgets deals with that.
/* size_t is a large, unsigned integer type big enough to contain the
theoretical maximum size of an object, so size functions often return
size_t.
strlen counts the amount of bytes before the first null (0) byte */
size_t n = strlen(name);
Now that we have the length of the string, we can check if the last byte is the newline character, and remove it if so.
/* Assuming every line ends with a newline, we can simply zero out the last
byte if it's '\n' */
if (name[n - 1] == '\n') {
name[n - 1] = '\0';
/* The string is now 1 byte shorter, because we removed the newline.
We don't need to calculate strlen again, we can just do it manually. */
--n;
}
The loop looks quite similar, as it was mostly fine to begin with. Mostly, we want to avoid issues that can arise from comparing a signed int and an unsigned size_t, so we'll also make i be type size_t.
for (size_t i = 0; i < n; i++) {
int e = name[i];
printf("The ASCII value of the letter %c is : %d \n", name[i], e);
}
Putting it all together, we get
#include <stdio.h>
#include <string.h>
int main() {
char name[100];
memset(name, 0, sizeof(name));
printf("Enter a name : \n");
fgets(name, sizeof(name), stdin);
size_t n = strlen(name);
if (n > 0 && name[n - 1] == '\n') {
name[n - 1] = '\0';
--n;
}
for (size_t i = 0; i < n; i++){
int e = name[i];
printf("The ASCII value of the letter %c is : %d \n", name[i], e);
}
/* To correctly print a size_t, use %zu */
printf("%zu\n", n);
/* In C99 main implicitly returns 0 if you don't add a return value
yourself, but it's a good habit to remember to return from functions. */
return 0;
}
Which should work pretty much as expected.
Additional notes:
This code should be valid C99, but I believe it's not valid C89. If you need to write to the older standard, there are several things you need to do differently. Fortunately, your compiler should warn you about those issues if you tell it which standard you want to use. C99 is probably the default these days, but older code still exists.
It's a bit inflexible to be reading strings into fixed-size buffers like this, so in a real situation you might want to have a way of dynamically increasing the size of the buffer as necessary. This will probably require you to use C's manual memory management functionality like malloc and realloc, which aren't particularly difficult but take greater care to avoid issues like memory leaks.
It's not guaranteed the strings you're reading are in any specific encoding, and C strings aren't really ideal for handling text that isn't encoded in a single-byte encoding. There is support for "wide character strings" but probably more often you'll be handling char strings containing UTF-8 where a single codepoint might be multiple bytes, and might not even represent an individual letter as such. In a more general-purpose program, you should keep this in mind.
If we need write a code to get ASCII values of all elements in a string, then we need to use "%d" instead of "%c". By doing this %d takes the corresponding ascii value of the following character.
If we need to only print the ascii value of each character in the string. Then this code will work:
#include <stdio.h>
char str[100];
int x;
int main(){
scanf("%s",str);
for(x=0;str[x]!='\0';x++){
printf("%d\n",str[x]);
}
}
To store all corresponding ASCII value of character in a new variable, we need to declare an integer variable and assign it to character. By this way the integer variable stores ascii value of character. The code is:
#include <stdio.h>
char str[100];
int x,ascii;
int main(){
scanf("%s",str);
for(x=0;str[x]!='\0';x++){
ascii=str[x];
printf("%d\n",ascii);
}
}
I hope this answer helped you.....😊
I am taking in 10 numbers from the user (user enters them at a prompt, and the numbers are separated by commas, as so: 245645, -243, 4245). How can I put these elements into an array? As shown below, I have used scanf which does not work as I had hoped. Any suggestions would be appreciated.
//User will pass ten numbers, separated by commas. This is to be put into an array.
#include <stdio.h>
int main ()
{
int A[10]; // array to contain in users input.
printf("Enter your numbers: ");
scanf("%d", &A[10]);
return 0;
}
You have to consume the comma as well in scanf:
for(int i=0; i<10; i++) { /* for each element in A */
if(0==scanf("%d,", &A[i])) { /* read a number from stdin into A[i] and then consume a commma (if any) */
break; /* if no digit was read, user entered less than 10 numbers separated by commas */
/* alternatively error handling if fewer than 10 is illegal */
}
}
I won't write the whole thing for you.
But I can definitely help.
One of the ways to do that will be:
Get a string that contains 10 comma-separated numbers: fgets() may be?
Validate the string, trim white-spaces as well, makes life easier
Pick out a number from string: strtol() may be?
Search for a ',' character in the string, and set pointer to the next index after ',': strchr() may be?
Repeat steps 3 and 4 for a total of 10 times (from here, 9 times actually)
Print the numbers
The code below would do half of your job. The only remaining part would be to get string from user and validate it.
The intention to have a string declared and initialised upfront is to put more emphasise on actual parsing of data which appear complicated to beginners (no offence).
Before we look at the code below, lets read a few things first.
You might want to take a look at the man page for strtol() function
You might want to take a look at the man page for fgets() function, which is not used in the code below, but you may end-up using it to achieve step 1.
I already concede the fact that this may not be the best way to achieve it, and I would happily agree that this code below can be made better in thousand ways by adding various error check, but I leave that to you to explore and implement.
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int main(void)
{
int i = 0, j = 0;
char *Str = "1,11,21,1211,111221,312211,1234,4321,123,789";
char *ptr;
long ret;
long array[10] = { [0 ... 9] = 0 };
// So, lets assume step 1 and 2 are taken care of.
// Iterate though the data for 10 times
for(i = 0; i < 10; i++)
{
ret = strtol(Str, &ptr, 10);
// Check if its a number
if(ret != 0)
{
// Its is a number!
// Put it in the array
array[j] = ret;
// Increment the index so that next number will not over-write the existing one
j++;
// Find the next ',' in the string
Str = strchr(Str, ',');
if(Str == NULL)
{
// Handle this condition that there are no more commas in the string!
break;
}
// Assuming that the ',' is found, increment the pointer to index next to ','
Str++;
}
}
// Print the array
for(i = 0; i < j; i++)
printf("%ld\n", array[i]);
}
This prints the following output:
1
11
21
1211
111221
312211
1234
4321
123
789
Hope I have got you started, Good luck.
I have a txt file that its lines are as follows
[7 chars string][whitespace][5 chars string][whitespace][integer]
I want to use fscanf() to read all these into memory, and I'm confused about what format should I use.
Here's an example of such line:
hello box 94324
Notice the filling whitespaces in each string, apart from the separating whitespace.
Edit: I know about the recommendation to use fgets() first, I cannot use it here.
Edit: here's my code
typedef struct Product {
char* id; //Product ID number. This is the key of the search tree.
char* productName; //Name of the product.
int currentQuantity; //How many items are there in stock, currently.
} Product;
int main()
{
FILE *initial_inventory_file = NULL;
Product product = { NULL, NULL, 0 };
//open file
initial_inventory_file = fopen(INITIAL_INVENTORY_FILE_NAME, "r");
product.id = malloc(sizeof(char) * 10); //- Product ID: 9 digits exactly. (10 for null character)
product.productName = malloc(sizeof(char) * 11); //- Product name: 10 chars exactly.
//go through each line in inital inventory
while (fscanf(initial_inventory_file, "%9c %10c %i", product.id, product.productName, &product.currentQuantity) != EOF)
{
printf("%9c %10c %i\n", product.id, product.productName, product.currentQuantity);
}
//cleanup...
...
}
Here's a file example: (it's actually 10 chars, 9 chars, and int)
022456789 box-large 1234
023356789 cart-small 1234
023456789 box 1234
985477321 dog food 2
987644421 cat food 5555
987654320 snaks 4444
987654321 crate 9999
987654322 pillows 44
Assuming your input file is well-formed, this is the most straightforward version:
char str1[8] = {0};
char str2[6] = {0};
int val;
...
int result = fscanf( input, "%7s %5s %d", str1, str2, &val );
If result is equal to 3, you successfully read all three inputs. If it's less than 3 but not EOF, then you had a matching failure on one or more of your inputs. If it's EOF, you've either hit the end of the file or there was an input error; use feof( input ) to test for EOF at that point.
If you can't guarantee your input file is well-formed (which most of us can't), you're better off reading in the entire line as text and parsing it yourself. You said you can't use fgets, but there's a way to do it with fscanf:
char buffer[128]; // or whatever size you think would be appropriate to read a line at a time
/**
* " %127[^\n]" tells scanf to skip over leading whitespace, then read
* up to 127 characters or until it sees a newline character, whichever
* comes first; the newline character is left in the input stream.
*/
if ( fscanf( input, " %127[^\n]", buffer ) == 1 )
{
// process buffer
}
You can then parse the input buffer using sscanf:
int result = sscanf( buffer, "%7s %5s %d", str1, str2, &val );
if ( result == 3 )
{
// process inputs
}
else
{
// handle input error
}
or by some other method.
EDIT
Edge cases to watch out for:
Missing one or more inputs per line
Malformed input (such as non-numeric text in the integer field)
More than one set of inputs per line
Strings that are longer than 7 or 5 characters
Value too large to store in an int
EDIT 2
The reason most of us don't recommend fscanf is because it sometimes makes error detection and recovery difficult. For example, suppose you have the input records
foo bar 123r4
blurga blah 5678
and you read it with fscanf( input, "%7s %5s %d", str1, str2, &val );. fscanf will read 123 and assign it to val, leaving r4 in the input stream. On the next call, r4 will get assigned to str1, blurga will get assigned to str2, and you'll get a matching failure on blah. Ideally you'd like to reject the whole first record, but by the time you know there's a problem it's too late.
If you read it as a string first, you can parse and check each field, and if any of them are bad, you can reject the whole thing.
Let's assume the input is
<LWS>* <first> <LWS>+ <second> <LWS>+ <integer>
where <LWS> is any whitespace character, including newlines; <first> has one to seven non-whitespace characters; <second> has one to five non-wihitespace characters; <integer> is an optionally signed integer (in hexadecimal if it begins with 0x or 0X, in octal if it begins with 0, or in decimal otherwise); * indicates zero or more of the preceding element; and + indicates one or more of the preceding element.
Let's say you have a structure,
struct record {
char first[8]; /* 7 characters + end-of-string '\0' */
char second[6]; /* 5 characters + end-of-string '\0' */
int number;
};
then you can read the next record from stream in into the structure pointed to by the caller using e.g.
#include <stdlib.h>
#include <stdio.h>
/* Read a record from stream 'in' into *'rec'.
Returns: 0 if success
-1 if invalid parameters
-2 if read error
-3 if non-conforming format
-4 if bug in function
+1 if end of stream (and no data read)
*/
int read_record(FILE *in, struct record *rec)
{
int rc;
/* Invalid parameters? */
if (!in || !rec)
return -1;
/* Try scanning the record. */
rc = fscanf(in, " %7s %5s %d", rec->first, rec->second, &(rec->number));
/* All three fields converted correctly? */
if (rc == 3)
return 0; /* Success! */
/* Only partially converted? */
if (rc > 0)
return -3;
/* Read error? */
if (ferror(in))
return -2;
/* End of input encountered? */
if (feof(in))
return +1;
/* Must be a bug somewhere above. */
return -4;
}
The conversion specifier %7s converts up to seven non-whitespace characters, and %5s up to five; the array (or char pointer) must have room for an additional end-of-string nul byte, '\0', which the scanf() family of functions add automatically.
If you do not specify the length limit, and use %s, the input can overrun the specified buffer. This is a common cause for the common buffer overflow bug.
The return value from the scanf() family of functions is the number of successful conversions (possibly 0), or EOF if an error occurs. Above, we need three conversions to fully scan a record. If we scan just 1 or 2, we have a partial record. Otherwise, we check if a stream error occurred, by checking ferror(). (Note that you want to check ferror() before feof(), because an error condition may also set feof().) If not, we check if the scanning function encountered end-of-stream before anything was converted, using feof().
If none of the above cases were met, then the scanning function returned zero or negative without neither ferror() or feof() returning true. Because the scanning pattern starts with (whitespace and) a conversion specifier, it should never return zero. The only nonpositive return value from the scanf() family of functions is EOF, which should cause feof() to return true. So, if none of the above cases were met, there must be a bug in the code, triggered by some odd corner case in the input.
A program that reads structures from some stream into a dynamically allocated buffer typically implements the following pseudocode:
Set ptr = NULL # Dynamically allocated array
Set num = 0 # Number of entries in array
Set max = 0 # Number of entries allocated for in array
Loop:
If (num >= max):
Calculate new max; num + 1 or larger
Reallocate ptr
If reallocation failed:
Report out of memory
Abort program
End if
End if
rc = read_record(stream, ptr + num)
If rc == 1:
Break out of loop
Else if rc != 0:
Report error (based on rc)
Abort program
End if
End Loop
The issue in your code using the "%9c ..."-format is that %9c does not write the string terminating character. So your string is probably filled with garbage and not terminated at all, which leads to undefined behaviour when printing it out using printf.
If you set the complete content of the strings to 0 before the first scan, it should work as intended. To achieve this, you can use calloc instead of malloc; this will initialise the memory with 0.
Note that the code also has to somehow consumes the newline character, which is solved by an additional fscanf(f,"%*c")-statement (the * indicates that the value is consumed, but not stored to a variable). Will work only if there are no other white spaces between the last digit and the newline character:
int main()
{
FILE *initial_inventory_file = NULL;
Product product = { NULL, NULL, 0 };
//open file
initial_inventory_file = fopen(INITIAL_INVENTORY_FILE_NAME, "r");
product.id = calloc(sizeof(char), 10); //- Product ID: 9 digits exactly. (10 for null character)
product.productName = calloc(sizeof(char), 11); //- Product name: 10 chars exactly.
//go through each line in inital inventory
while (fscanf(initial_inventory_file, "%9c %10c %i", product.id, product.productName, &product.currentQuantity) == 3)
{
printf("%9s %10s %i\n", product.id, product.productName, product.currentQuantity);
fscanf(initial_inventory_file,"%*c");
}
//cleanup...
}
Have you tried the format specifiers?
char seven[8] = {0};
char five[6] = {0};
int myInt = 0;
// loop here
fscanf(fp, "%s %s %d", seven, five, &myInt);
// save to structure / do whatever you want
If you're sure that the formatting and strings are the always fixed length, you could also iterate over input character by character (using something like fgetc() and manually process it. The example above could cause segmentation errors if the string in the file exceeds 5 or 7 characters.
EDIT Manual Scanning Loop:
char seven[8] = {0};
char five[6] = {0};
int myInt = 0;
// loop this part
for (int i = 0; i < 7; i++) {
seven[i] = fgetc(fp);
}
assert(fgetc(fp) == ' '); // consume space (could also use without assert)
for (int i = 0; i < 5; i++) {
five[i] = fgetc(fp);
}
assert(fgetc(fp) == ' '); // consume space (could also use without assert)
fscanf(fp, "%d", &myInt);
so i've been writing a program that convert a decimal number to it's boolean representation but every time i compile the return value which is a string show additional characters like p┐ here is the program
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
void main (void)
{
signed char str[256];
int dec,rest;
int i = -1;
int j;
printf ("write a decimal number : ");
scanf ("%d",&dec);
do
{
rest = dec % 2;
dec/= 2;
for (j=i;j>-1;--j)
str[j+1]=str[j];
str[0]=rest+48;
++i;
} while (dec!=0);
printf ("the binary representation of this number is %s",str);
}
the output :
write a decimal number : 156
the binary representation of this number is 10011100p┐
i don't know if im missing something but i will be grateful if you guys help me
In C and C++, strings are null-terminated, this means that every valid string must end with a character with code 0. This character tells every function that is dealing with this string that it is in fact over.
In your program you create a string, signed char str[256]; and it is initially filled with random data; this means that you reserved space for 256 characters and they are all garbage, but the system does not know they are invalid. Try printing this string and see what happens.
In order to actually tell the system that your string is over after say, 8 characters, the 9th character hast to be the NUL character, or simply 0. In your code you can do it in two ways:
after the loop, assign str[i] = 0, or (even simpler)
initialize the string as signed char str[256]={0};, whiche creates the storage and fills it with nulls; after writing to the string you can be sure that the character after the last one you've written will be a NUL.
At the end of your do {} while () loop, you need to set the character after the last character in your string to 0. This is the array index of the last character you want (i) plus one. This lets printf know where your string ends. (Otherwise, how could it know?)
initialize the str variable to NUL.
void main (void)
{
signed char str[256];
int dec,rest;
int i = -1;
int j;
memset( str, '\0', sizeof(str) );
printf ("write a decimal number : ");
scanf ("%d",&dec);
do
{
rest = dec % 2;
dec/= 2;
for (j=i;j>-1;--j)
str[j+1]=str[j];
str[0]=rest+48;
++i;
} while (dec!=0);
printf ("the binary representation of this number is %s",str);
}
I am currently learning C, and so I wanted to make a program that asks the user to input a string and to output the number of characters that were entered, the code compiles fine, when I enter just 1 character it does fine, but when I enter 2 or more characters, no matter what number of character I enter, it will always say there is just one character and crashes after that. This is my code and I can't figure out what is wrong.
int main(void)
{
int siz;
char i[] = "";
printf("Enter a string.\n");
scanf("%s", i);
siz = sizeof(i)/sizeof(char);
printf("%d", siz);
getch();
return 0;
}
I am currently learning to program, so if there is a way to do it using the same scanf() function I will appreciate that since I haven't learned how to use any other function and probably won't understand how it works.
Please, FORGET that scanf exists. The problem you are running into, whilst caused mostly by your understandable inexperience, will continue to BITE you even when you have experience - until you stop.
Here is why:
scanf will read the input, and put the result in the char buffer you provided. However, it will make no check to make sure there is enough space. If it needs more space than you provided, it will overwrite other memory locations - often with disastrous consequences.
A safer method uses fgets - this is a function that does broadly the same thing as scanf, but it will only read in as many characters as you created space for (or: as you say you created space for).
Other observation: sizeof can only evaluate the size known at compile time : the number of bytes taken by a primitive type (int, double, etc) or size of a fixed array (like int i[100];). It cannot be used to determine the size during the program (if the "size" is a thing that changes).
Your program would look like this:
#include <stdio.h>
#include <string.h>
#define BUFLEN 100 // your buffer length
int main(void) // <<< for correctness, include 'void'
{
int siz;
char i[BUFLEN]; // <<< now you have space for a 99 character string plus the '\0'
printf("Enter a string.\n");
fgets(i, BUFLEN, stdin); // read the input, copy the first BUFLEN characters to i
siz = sizeof(i)/sizeof(char); // it turns out that this will give you the answer BUFLEN
// probably not what you wanted. 'sizeof' gives size of array in
// this case, not size of string
// also not
siz = strlen(i) - 1; // strlen is a function that is declared in string.h
// it produces the string length
// subtract 1 if you don't want to count \n
printf("The string length is %d\n", siz); // don't just print the number, say what it is
// and end with a newline: \n
printf("hit <return> to exit program\n"); // tell user what to do next!
getc(stdin);
return 0;
}
I hope this helps.
update you asked the reasonable follow-up question: "how do I know the string was too long".
See this code snippet for inspiration:
#include <stdio.h>
#include <string.h>
#define N 50
int main(void) {
char a[N];
char *b;
printf("enter a string:\n");
b = fgets(a, N, stdin);
if(b == NULL) {
printf("an error occurred reading input!\n"); // can't think how this would happen...
return 0;
}
if (strlen(a) == N-1 && a[N-2] != '\n') { // used all space, didn't get to end of line
printf("string is too long!\n");
}
else {
printf("The string is %s which is %d characters long\n", a, strlen(a)-1); // all went according to plan
}
}
Remember that when you have space for N characters, the last character (at location N-1) must be a '\0' and since fgets includes the '\n' the largest string you can input is really N-2 characters long.
This line:
char i[] = "";
is equivalent to:
char i[1] = {'\0'};
The array i has only one element, the program crashes because of buffer overflow.
I suggest you using fgets() to replace scanf() like this:
#include <stdio.h>
#define MAX_LEN 1024
int main(void)
{
char line[MAX_LEN];
if (fgets(line, sizeof(line), stdin) != NULL)
printf("%zu\n", strlen(line) - 1);
return 0;
}
The length is decremented by 1 because fgets() would store the new line character at the end.
The problem is here:
char i[] = "";
You are essentially creating a char array with a size of 1 due to setting it equal to "";
Instead, use a buffer with a larger size:
char i[128]; /* You can also malloc space if you desire. */
scanf("%s", i);
See the link below to a similar question if you want to include spaces in your input string. There is also some good input there regarding scanf alternatives.
How do you allow spaces to be entered using scanf?
That's because char i[] = ""; is actually an one element array.
Strings in C are stored as the text which ends with \0 (char of value 0). You should use bigger buffer as others said, for example:
char i[100];
scanf("%s", i);
Then, when calculating length of this string you need to search for the \0 char.
int length = 0;
while (i[length] != '\0')
{
length++;
}
After running this code length contains length of the specified input.
You need to allocate space where it will put the input data. In your program, you can allocate space like:
char i[] = " ";
Which will be ok. But, using malloc is better. Check out the man pages.