A Few Useful Notes on C for Assignment 8


1.  Arrays - which you'll need for sorting: 

    To declare an integer array:    int A[100];
    To declare a real array:        double Y[100];
    To declare a character array, which is a string:     char S[100];

    - Arrays are numbered from 0, so there are elements A[0], A[1], ... A[99].

    - That is also how you access the elements: e.g.  T = A[34];

    - The only difference from Turing is the square brackets and the enforced
      numbering of the index from 0.

2.  Formatted output:  (the equivalent of put)

    Be sure to put: #include <stdio.h> 
    at the top of your program.

    Output is done with the printf function which has the rough syntax:

               printf("<format string>", var1, var2, ....);

    To print an integer:	int Lvar;
				Lvar = 5;
				printf("This is an integer: %d\n", Lvar);

	- this will print:  This is an integer: 5
	- the %d in the format string tells the function to look for an integer 
	  variable following the <format string>, and put it where the %d
	  was in the format string.

	- for floats an doubles, use %f
	- for strings use %s

    To print an integer and then a real and then a string:

	int Intvar = 4;
	double Fvar = 2.3;
	char Svar[100] = "String Example";

	printf("The integer is %d, the real is %d and the string is %s\n",
			Intvar, Fvar, Svar);

    This will print: The integer is 4, the real is 2.3 and the string is String Example

3.  Input:  - also need to include stdio.h as above

	    - use the scanf function: scanf("<format string>", pvar1, pvar2 ..);

	    - as with printf the format string indicates the type of variables
	      to read from the terminal.
	
	    - the tricky part, which I'll explain later next week, is that
	      the "pvar1,.."   have to be *pointers* to the variables  you
	      want to input, not the variables themselves.

	    - to get a pointer to a variable X, you just put an
	      ampersand in front of it:

		   e.g. &X
	
	    - so to input an integer X using scanf:

		 int X;

		 scanf("%d",&X);

	    - this is equivalent to "get X" in Turing.   If you want to input
	      a real, then use %f, and a string, then use %s.

	    - to input an integer and then a real and then a string:

		int X;
		double Y;
		char S[100];   /*  a string is an array of char */

		scanf ("%d %f %s", &X, &Y, S);

		Note a special case here:  if you use the name of an array
		without an index, it is actually a  pointer to the first element
		of the array.   Instead of S above, I could have used
		 &(S[1]), which points to the same thing

	I hope this helps!

				Jonathan