I have the task to count the number of letters in random words until "End" is entered. I'm not allowed to use the strlen(); function. That's my solution so far:
#include <stdio.h>
#include <string.h>
int stringLength(char string[]){
unsigned int length = sizeof(*string) / sizeof(char);
return length;
}
int main(){
char input[40];
while (strcmp(input, "End") != 0) {
printf("Please enter characters.\n");
scanf("%s", &input[0]);
while (getchar() != '\n');
printf("You've entered the following %s. Your input has a length of %d characters.\n", input, stringLength(input));
}
}
The stringLength value isn't correct. What am I doing wrong?
The %n specifier could also be used to capture the number of characters.
Using %39s will prevent writing too many characters into the array input[40].
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main( void)
{
char input[40] = {'\0'};
int count = 0;
do {
printf("Please enter characters or End to quit.\n");
scanf("%39s%n", input, &count);
while (getchar() != '\n');
printf("You've entered the following %s. Your input has a length of %d characters.\n", input, count);
} while (strcmp(input, "End") != 0);
return 0;
}
EDIT to correct flaw pointed out by #chux.
using " %n to record leading space and %n" record total characters this should record the number of leading whitespace and the total characters parsed.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main( int argc, char *argv[])
{
char input[40] = {'\0'};
int count = 0;
int leading = 0;
do {
printf("Please enter characters. Enter End to quit.\n");
if ( ( scanf(" %n%39s%n", &leading, input, &count)) != 1) {
break;
}
while (getchar() != '\n');
printf("You've entered %s, with a length of %d characters.\n", input, count - leading);
} while (strcmp(input, "End") != 0);
return 0;
}
EDIT stringLength() function to return length
int stringLength(char string[]){
unsigned int length = 0;
while ( string[length]) {// true until string[length] is '\0'
length++;
}
return length;
}
Please note that sizeof is evaluated at compile time. So it can't be used to determine the length of a string in run time.
The length of a string is the number of characters until you encounter a null-character. The size of a string is thus one more than the number of characters. This final null-character is called the terminating null character.
So to know the length of a string in run-time, you have to count the number of characters until you encounter a null-character.
Programming this in C is simple; I leave this to you.
Related
I am just running a code to find the length of a given string input by the user in C programming language. I used a loop condition to determine the length but statements inside loop executes when the condition is false also. The code I have tried in c is:
#include <stdio.h>
#define ArrayLength 50
int StringLengthCount();
int main() {
printf("Hello, World!\n");
/*Question: Find inserted string's length, without build in function*/
int c=StringLengthCount();
printf("Your inserted string's length is:%d",c);
return 0;
}
int StringLengthCount(){
printf("\n");
printf("Please enter a sentence to find its length of character:");
char array1[ArrayLength];
fgets(array1,ArrayLength,stdin);
printf("Your inserted string is:%s\n",array1);
int i=0;
int count=0;
while(array1[i]!='\0'){
count++;
printf("%d character is %c",count,array1[i]);
printf("\n");
i++;
}
printf("\n");
printf("Your inserted string's total character i.e string length is:%d",count);
}
I am expecting the result 2 for a sample string input "we", but it gives result 3.
The output result in CLion compiler is given below
enter image description here
Can you kindly tell me why it happens?
If by "statements inside loop executes when the condition is false also" you mean that you see an extra character every time you execute remember that also the line feed (LF alias \n) character that you use to enter your string is part of the acquired string.
So even the empty string has one character that is \n or 0x10.
Your check should be something like this:
while (array1[len] != '\0' && array1[len] != '\n' )
And you function, as suggested in the comments, should have a return and could use just one variable like this:
int StringLengthCount() {
printf("\n");
printf("Please enter a sentence to find its length of character:");
char array1[ArrayLength];
fgets(array1, ArrayLength, stdin);
printf("Your inserted string is:%s\n", array1);
int len = 0;
while (array1[len] != '\0' && array1[len] != '\n' ) {
printf("%d character is %c", len + 1, array1[len]);
printf("\n");
len++;
}
printf("\n");
printf("Your inserted string's total character i.e string length is:%d\n\n",
len);
return len;
}
The function fgets will also read the newline character, so you need to change the condition in the while-loop from str[i] != '\0' to str[i] != '\n'. I have also implemented the suggested changes by Devolus.
#include <stdio.h>
#include <stdlib.h>
#define LEN 50
void string_length();
int main(void)
{
string_length();
return EXIT_SUCCESS;
}
void string_length(void)
{
printf("Enter a string: ");
char str[LEN];
fgets(str, LEN - 1, stdin);
printf("Your entered string is: %s\n", str);
int i = 0;
while (str[i] != '\n') {
printf("The %d. character is '%c'.\n", i + 1, str[i]);
++i;
}
printf("\nThe string's length is %d.\n", i);
}
This might be a rookie question, but I need to make sure that the input given by the user is of data type char [%c] or a string [%s].
If it were an integer, I would just do something like this:
int data, x;
do {
printf("Please enter a number: ");
x = scanf(" %d", &data);
getchar();
} while(x!=1);
So I was wondering if there's a similar way to do this, if the input is supposed to be a string or a character. Thanks, Any help would be appreciated!
Avoid to use %c in scanf() because some unexpected character like \r\n will be input.
You can use a char[2] to receive a single character. An \0 will be filled after your string to represent the end of string, so the length of array must be bigger than 1.
An example:
#include <stdio.h>
int main()
{
char data[2];
scanf("%1s", data);
if (data[0] >= 'a' && data[0] <= 'z') // custom your constraint here
{
// legal
printf("legal: %s", data);
}
else
{
// illegal
printf("illegal: %s", data);
}
return 0;
}
While I input b, the data will be "b\0".
part of the answer is if you just want to read only alphabet you can use below.
#include <stdio.h>
#include <ctype.h>
int main()
{
char ch;
do {
printf("enter a char:");
scanf(" %c",&ch);
}while(!isalpha(ch));
printf("%c",ch);
return 0;
}
Update 1:
Just for the completeness and for the FUN part of the programing, have added code here.
This works well (not tested robustly, you can do if you need to) for the single char input or for a string of length 9.
Remember to type the EOF after input is entered in case length of input is < 9.
and read EOF behavior on same line and new line.
#include <stdio.h>
#include <ctype.h>
#define LEN 10
int main()
{
char ch;
char str[LEN] = {0};
int i = 0;
int ret;
printf("enter a char or string(len = 9) and press EOF if len < 9\n");
do {
if(1== (ret = scanf(" %c",&ch)))
{
if(isalpha(ch))
str[i++] = ch;
}
else
printf("scanf:Error (%d)\n", ret);
}while(ret != EOF && ( !isalpha(ch) || i < LEN-1));
str[i] = '\0';
printf("str is %s\n",str);
return 0;
}
Actually, I can easily found a similar question in Google, but it still can not solve my question.
How to prevent non-numeric input in C?
The upper-link is like a similar case.
Here is my code
#include <stdio.h>
int main()
{
int n;
printf("Enter 1 or 2?\n");
scanf("%d", &n);
while(n != 1 && n != 2)
{
printf("Please do not enter other characters\n");
printf("Enter 1 or 2?\n");
scanf("%d", &n);
}
}
I hope if users enter other numbers(e.g. 1, 45, 656), characters (e.g. a, f, u, e), or string(e.g. apple), the upper program can print out an error message and ask for user input again.
Yes! if users enter other numbers, the program can do what I want.
But! if users enter other characters, string, the program will keep looping.
What should I need to add to this program?
How to prevent non-numeric input in C & ask user input again
Do not use scanf()**. Use fgets().
scanf("%d", ...) does not consume non-numeric input. Instead that offending input remains in stdio for the next scanf().
Code cannot prevent non-numeric input unless it locks the keys from being pressed. Instead, read all input, identify the non-numeric text, toss it and present the user with feedback for new input.
Make a helper function to control impact on rest of code.
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
// return -1 on EOF
int read_int_in_range(const char *prompt, const char *reprompt, int lo, int hi) {
if (prompt) {
fputs(prompt, stdout);
fflush(stdout);
}
char buf[100];
while (fgets(buf, sizeof buf, stdin)) {
char *endptr;
errno = 0;
long val = strtol(buf, &endptr, 10);
// no overflow, conversion occurred, in range
if (errno == 0 && endptr > buf && val >= lo && val <= hi) {
// Tolerate trailing white-space.
while (isspace((unsigned char ) *endptr)) {
endptr++;
}
// No junk after the numeric text
if (*endptr == '\0') {
return (int) val;
}
}
if (reprompt) {
fputs(reprompt, stdout);
fflush(stdout);
}
}
return EOF; // or `INT_MIN` or TBD code to distinguish `int` from an error.
}
Usage
const char *prompt = "Enter 1 or 2?\n";
const char *reprompt = "Please do not enter other characters\n" "Enter 1 or 2?\n";
int n = read_int_in_range(prompt, reprompt, 1, 2);
**I recommend to not use scanf() anywhere to read user input until ones understands its weaknesses and limitations.
scanf is meant for formatted input, ie: you know what input will be received, in this case the user may enter something other than an int and your program breaks down. So to deal with that unknown treat the input as a string then analyze the string. In this case you could capture the input in buf and use the function atoi to convert it to an int, like this:
#include <stdio.h>
#include <stdlib.h> /* for atoi */
int main()
{
int n;
char buf[10]; /* this is new */
printf("Enter 1 or 2\n");
/*scanf("%d", &n);*/
fgets(buf, 10, stdin);
n = atoi(buf);
while(n != 1 && n != 2)
{
printf("Please do not enter other characters\n");
printf("Enter 1 or 2?\n");
/*scanf("%d", &n);*/
fgets(buf, 10, stdin);
n = atoi(buf);
}
}
fgets is the way to do this, but wanted to post something like this to actually avoid fgets as asked. It may be of some interest. The appending part should've been delegated to some function and buffer size may've not been 10. Anyways:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define endl "\n"
int main (void)
{
int my_char = 0;
short bad = 0;
char text[10];
memset (text, 0, 10);
printf ("enter number: ");
while ( (my_char = getchar()) )
{
if ( my_char < '0' || my_char > '9' )
{
if ( my_char != '\n' ) bad = 1;
}
else
{
size_t len = strlen (text);
char *strtemp = malloc (len + 2);
strcpy (strtemp, text);
strtemp [len] = my_char;
strtemp [len + 1] = '\0';
strncpy (text, strtemp, 9);
free (strtemp);
}
if ( my_char == '\n' )
{
if ( bad )
{
printf ("enter again (just numbers): ");
fflush (stdout);
bad = 0;
memset (text, 0, 9);
}
else break;
}
}
printf ("entered: %s"endl, text);
}
I am trying to read the number of characters including, the spaces.
I use the scanf function to check for chars using %c. Also on a side note, how would I go about storing the input into an array?
#include <stdio.h>
int main(void) {
char n, count= 0;
while (scanf("%c", &n) != EOF) {
count = count+1;
}
printf("%d characters in your input \n", count);
return 0;
}
When I test input (with spaces) such as
abcdefg
it doesn't print anything.
Defining a MAX_CHAR and checking that in loop would protect you against invalid memory write.
Remember that last byte of an array should be left for '\0', if you want to print or use the char array.
#include <stdio.h>
#define MAX_CHAR 100
int main(void) {
char n[MAX_CHAR]={0}, count= 0;
while((count!=MAX_CHAR-1)&&(scanf("%c",&n[count])==1))
{
if((n[count]=='\n')){
n[count]=0;
break;
}
count++;
}
printf("%d characters in your input [%s]\n", count, n);
return 0;
}
scanf does return EOF when it reaches the end of the file. But in order for you to see that happening, you should give your program a file input when you call it like this:
./a.out < input.txt
Inside input.txt you could put any text you want. But if you want to work in the command line, you should read until you find a \n
#include <stdio.h>
int main(void) {
char n, count = 0;
scanf("%c", &n);
while (n != '\n') {
count = count+1;
scanf("%c", &n);
}
printf("%d characters in your input \n", count);
return 0;
}
If you want to store the input in an array, you must know the size of the input (or at least the maximum size possible)
#include <stdio.h>
int main(void) {
char n, count = 0;
char input[100]; //the max input size, in this case, is 100
scanf("%c", &n);
while (n != '\n') {
scanf("%c", &n);
input[count] = n; //using count as the index before incrementing
count = count+1;
}
printf("%d characters in your input \n", count);
return 0;
}
Furthermore, if don't know the size or max size of the input, you'd have to dynamically change the size of the input array. But I think that would be a little advanced for you right now.
Your printf doesn't print anything because runtime doesn't reach to it. Your code looping for ever in while loop
while (scanf("%c", &n) != EOF) {
count = count+1;
}
because scanf won't return EOF in this case
I am reading the string from the stdin using fgets function and then trying to print the length of the string, But I am always getting the length of the string as 1 always for the first time
Here is my code
#incldue<stdio.h>
#include<string.h>
int main(void)
{
printf("\n Enter the no of test cases");
scanf("%d",&t);
int i,j;
for(i=0;i<t;++i)
{
char song[500],val[28];
int k=0,x=0;
fgets(song,500,stdin);
int len=strlen(song);
printf("\nlen=%d",len);
}
return 0;
}
I am always getting 1 as the length for the first test case :/
Please suggest where i am going wrong
You are not clearing the input buffer. After giving the input value to first scanf newline will be there. So fgets will not get the input from the user.
Newline will be placed in that buffer in a first(song[0]) position. So this is the reason strlen returns as value 1.
Make this line before the fgets.
int c;
if ( i == 0 )
while((c=getchar()) != '\n' && c != EOF );
fgets(song,500,stdin);
Or else place this line after getting the input from the scanf.
scanf("%d",&t);
while((c=getchar()) != '\n' && c != EOF );
Include \n in scanf input string (and in C declare variables at the beginning of the block { }).
Also notice the len will include the \n char.
#include<stdio.h>
#include<string.h>
int main(void)
{
int t, i;
printf("Enter the no of test cases: ");
scanf("%d\n",&t);
for(i=0;i<t;++i) {
char song[500];
int len;
fgets(song,500,stdin);
len=strlen(song);
printf("len=%d\n",len);
}
return 0;
}
update
If you need to handle weird input just use fgets (\n removed from len).
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int main(void)
{
char song[500];
int t, i, len;
printf("Enter the no of test cases: ");
fgets(song,500,stdin);
t = atoi(song);
for(i=0;i<t;++i) {
fgets(song,500,stdin);
if ((len=strlen(song)) > 0) {
song[--len] = '\0';
printf("len=%d\n",len);
}
}
return 0;
}
When using scanf (or its relatives), it is important to check the return of the function. scanf returns the number of input values correctly matched and assigned. If there are inappropriate characters or insufficient characters, scanf will experience a matching or input failure. A quick if statement will suffice:
if (!scanf ("%d", &t)) {
fprintf (stderr, "error: invalid type or number for test cases.\n");
return 1;
}
As also noted, fgets will read and include in song the trailing newline character. Generally, you will want to remove the trailing newline to prevent having stray newlines scattered through various strings within your code. (not to mention looking at a length=5 for data is a bit strange) A simple method for removing the newline after your call to fgets is:
len = strlen (song);
while (len && song[len-1] == '\n') /* strip newline */
song[--len] = 0;
Putting together the test of scanf return, emptying the input buffer, and stripping the newline after fgets, your code would look similar to:
#include <stdio.h>
#include <string.h>
int main (void)
{
int c = 0;
int i = 0;
int t = 0;
printf ("\n Enter the no of test cases: ");
if (!scanf ("%d", &t)) {
fprintf (stderr, "error: invalid type or number for test cases.\n");
return 1;
}
while ((c = getchar()) != '\n' && c != EOF);
for (i = 0; i < t; ++i) {
char song[500] = { 0 };
size_t len = 0;
if (printf ("\n case [%d] : ", i) && fgets (song, 500, stdin))
{
len = strlen (song);
while (len && song[len-1] == '\n') /* strip newline */
song[--len] = 0;
}
printf (" len : %zu\n", len);
}
printf ("\n");
return 0;
}
Output
$ ./bin/scanf_rd_int
Enter the no of test cases: 2
case [0] : this is case one - 28 chars.
len : 28
case [1] : this is case two -- 29 chars.
len : 29