Scanf reads only one word from sentence

Question

I'm new at C and I have a little problem. I need to write a program where the user enters text and the program shows how long it is.

I tried with strlen(), but it's not what I want.

char a[20];
scanf("%s",a)

And if I type "Hello world" the result is 5, but I need 11.

I need to use scanf, but maybe it's impossible to do that with it...

Answer 1

This call

scanf("%s",a)

fills the character array a until a white space is encountered. So this call will read only the word "Hello" and the input buffer will still keep the second word "world".

You can use either

char a[20];
scanf("%19[^\n]",a );
size_t n = strlen( s );
printf( "%zu\n", n );

Here is a demonstrative program

#include <stdio.h>
#include <string.h>

int main(void) 
{
    char a[20] = "";
    
    scanf( "%19[^\n]", a );
    
    size_t n = strlen( a );
    
    printf( "%zu: %s\n", n, a );
    
    return 0;
}

If to enter

Hello world

then the output is

11: Hello world

or

char a[20];

fgets( a, sizeof( a ), stdin );
a[strcspn( a, "\n" )] = '\0';

size_t n = strlen( s );
printf( "%zu\n", n );

Here is a demonstrative program.

#include <stdio.h>
#include <string.h>

int main(void) 
{
    char a[20] = "";
    
    fgets( a, sizeof( a ), stdin );
    a[strcspn( a, "\n" )] = '\0';
    
    size_t n = strlen( a );
    
    printf( "%zu: %s\n", n, a );
    
    return 0;
}

Again if to enter

Hello world                               

then the output will be the same as shown above

11: Hello world