Find length of a string in C (problem)

Question

5.00/5 (1 vote)

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Hello!!!
I have a problem in C code.
I read an input from user and I want to extract input's length using pointer,but I receive some errors in terminal.

Thanks in advance...

Error:

find_string_length_pointer.c: In function ‘main’:
find_string_length_pointer.c:10:24: error: invalid initializer
     char user_in[50] = user_input();
                        ^~~~~~~~~~
find_string_length_pointer.c: In function ‘user_input’:
find_string_length_pointer.c:20:13: warning: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[50]’ [-Wformat=]
     scanf("%s" , &user_input);
            ~^    ~~~~~~~~~~~
find_string_length_pointer.c:21:12: warning: return makes integer from pointer without a cast [-Wint-conversion]
     return user_input;
            ^~~~~~~~~~
find_string_length_pointer.c:21:12: warning: function returns address of local variable [-Wreturn-local-addr]

What I have tried:

C

#include <stdio.h>


char user_input();
int length_input(char *str_input);


int main(void)
{
    char user_in[50] = user_input();
    int str_length = length_input(user_in);
    printf("Length of input: %s , is: %d." , user_in , str_length);
}


char user_input()
{
    char user_input[50];
    printf("Give a letter/string/sentence to find it length: ");
    scanf("%s" , &user_input);
    return user_input;
}


int length_input(char *str_input)
{
    int length = 1;
    while(*str_input != '\0')
    {
        length++;
        str_input++;
    }
    return length;
}

Posted 26-Jul-20 9:29am

Nick_is_asking

Updated 26-Jul-20 10:06am

CPallini

v2

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Comments

Richard MacCutchan 27-Jul-20 3:49am

Why not use strlen which does it for you?

3 solutions

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Greg Utas · Accepted Answer · 2020-07-26T09:36:00

Solution 1

Your user_input function declares the array user_input as a local variable. When this function returns, that data disappears! You need to pass user_in (in main) as an argument to the user_input function.

Although it isn't an error, using the same name (user_input) for a function and a local variable in that function is confusing.

You may have more errors, but that was the first thing I noticed.

With regard to length_input, C provides the function strlen to find the length of a string.

Posted 26-Jul-20 9:36am

Greg Utas

Updated 26-Jul-20 9:49am

v4

Comments

Greg Utas 26-Jul-20 15:42pm

You need to pass user_in to your user_input function, the same as you pass it to your length_input function.

EDIT: Most (or all) of the errors that you get when compiling are because user_input is returning a char, which you then try to assign to a char array.

CPallini 26-Jul-20 15:51pm

5.

Rick York · Accepted Answer · 2020-07-26T09:59:00

Mr. Utas is on the right track. You have it pretty close but it needs a few changes. Here is one way :

C++

void get_input( char * input )
{
    printf( "Enter a string to find its length: " );
    scanf( "%s", input );
}

int main( void )
{
    int str_length = 0;
    char user_in[ 50 ] = { 0 }

    get_input( user_in );
    str_length = length_input( user_in );
    printf( "Length of input: '%s' is: %d\n" , user_in , str_length );
}

Your length function looks ~~OK.~~ has a problem : it should initialize length to zero.

CPallini · Accepted Answer · 2020-07-26T10:05:00

In order to fix the errors in your program, following the suggestions of Greg Utas, you might write

C

#include <stdio.h>

void user_input(char * str_input);
int length_input(char *str_input);

int main(void)
{
  char user_in[50];
  user_input( user_in );
  int str_length = length_input(user_in);
  printf("Length of input: %s , is: %d." , user_in , str_length);

  return 0;
}

void user_input(char * str_input)
{
  printf("Give a letter/string/sentence to find it length: ");
  scanf("%s" , str_input);
}

int length_input(char *str_input)
{
  int length = 0;
  while(*str_input != '\0')
  {
    length++;
    str_input++;
  }
   return length;
}

This would work, but, unfortunately the user_input function is not robust: scanf could overrun your buffer. See How to prevent scanf causing a buffer overflow in C? - Stack Overflow[^] for workarounds.

Find length of a string in C (problem)

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