Introductory Program

I l @ ve RuBoard

Introductory Program

By now, you probably expect a sample program at the beginning of each chapter, and I won't disappoint you. Listing 4.1 presents a program that engages in a dialogue with the user .

Listing 4.1 The talkback.c program.

 /* talkback.c -- nosy, informative program */ #include <stdio.h> #include <string.h>      /* for strlen() prototype         */ #define DENSITY 62.4     /* human density in lbs per cu ft */ int main(void) {   float weight, volume;   int size, letters;   char name[40];         /* name is an array of 40 chars   */   printf("Hi! What's your first name?\n");   scanf("%s", name);   printf("%s, what's your weight in pounds?\n", name);   scanf("%f", &weight);   size = sizeof name;   letters = strlen(name);   volume = weight / DENSITY;   printf("Well, %s, your volume is %2.2f cubic feet.\n",        name, volume);   printf("Also, your first name has %d letters,\n",        letters);   printf("and we have %d bytes to store it in.\n", size);   return 0; } 

(Recall that some compilers, such as Think C for the Macintosh, require %ld for printing sizeof quantities .) Running talkback produces results such as the following:

 Hi! what's your first name?  Angelica  Angelica, what's your weight in pounds?  132.5  Well, Angelica, your volume is 2.12 cubic feet. Also, your first name has 8 letters, and we have 40 bytes to store it in. 

Here are the main new features of this program:

• It uses an array to hold a character string . Here, someone's name is read into the array, which, in this case, is a series of 40 consecutive bytes in memory, each able to hold a single character value.

• It uses the %s conversion specification to handle the input and output of the string. Note that name , unlike weight , does not use the & prefix when used with scanf() . (As you'll see later, both &weight and name are addresses.)

• It uses the C preprocessor to define the symbolic constant DENSITY to represent the value 62.4 .

• It uses the C function strlen() to find the length of a string.

The C approach might seem a little complex compared with the input/output of, say, BASIC. However, this complexity buys a finer control of I/O and a greater program efficiency. It is surprisingly easy once you get used to it.

Let's investigate these new ideas.

I l @ ve RuBoard