C

j0hnsmith · 05-03-2009, 02:13 AM

I'm learning C and have a problem that I can't work out.

You can declare an int and give it a new value any time you like but I can't do the same with a string. I want to change only the value of the string, not the size of string the variable can contain.

Code:

#include <stdio.h>

void main(void){ 
	
  int number; // declare
  number = 10; // assign value

  char test[100]; // declare

  printf("Please enter a word: ");
  scanf("%s", test);
	
  printf("sizeof test: %d\n", sizeof(test)); // still 100
  printf("%s\n", test);

  test = "fails"; // error - cannot convert from 'char [6]' to 'char [100]'. I don't want to change the size, only assign a new value (scanf is doing this).

}

aspire1 · 05-03-2009, 02:42 AM

#include <string.h>

char *strcpy( char *s1, const char *s2)

*copies the string s2 into the character array s1. The value of s1 is returned.

j0hnsmith · 05-03-2009, 07:27 AM

Thanks

theNbomr · 05-03-2009, 12:27 PM

Quote:

Originally Posted by aspire1

#include <string.h>

char *strcpy( char *s1, const char *s2)

*copies the string s2 into the character array s1. The value of s1 is returned.

While that seems to solve j0hnsmiths problem, it still leaves him with the essential question unanswered.

In one place, he has declared an array of 100 char's, and called it 'test'. We are allowed to use the shorthand notation of referring to the address of the zeroth element of the array by simply using the variable name (the ultimate cause of this confusion). Nevertheless, the array is still 100 char's.
Later in the code, j0hnsmith tries to make an assignment to the array of 100 chars called test. In the assignment, he says 'make the address of the zeroth element of the 100 char's equal to the address of the literal string "fails"'. Since this cannot happen, the compiler bails.
This shorthand use of arrays by name probably causes more confusion than any other issue in the C language. It is a convenience to those who understand it, but a tripping point to those who do not.

--- rod

j0hnsmith · 05-03-2009, 11:28 PM

Thanks theNbomr, your explanation is very useful although I did realise that something like this was happening.

C takes a lot more thought compared to PHP and JavaScript