Page 92 - Programming Microcontrollers in C

Pointers 77

written to the screen when the program is executed. A command line
can be read by the program. The definition of the program name main
when extended to read in a command line is as follows

void main ( int argc, char *argv[])

The integer variable argc is the number of entries on the command line.
The array of pointers to the type char argv[] contains pointers to
strings. When entering arguments onto the command line, they must be
separated by spaces. The first string pointed to by argv[0] is the name
of the program from the command line. The successive pointer values
point to additional character strings. These strings are each 0 terminated,
and they point to the successive entries on the command line. The value of
argc is the total number of command line entries including the program
name. It must be remembered that each entry in argv[] is a pointer to a
string. Therefore, if a number is entered on the command line, it must be
converted from a string to an integer, or floating point number, prior to its
use in the program. Let us see how this concept can be used. Earlier, we
wrote a function to calculate a Fibonacci number. Let’s use this function in
a program in which the argument for the Fibonacci calculation is read in
from the command line:

#include <stdio.h>
#include <stdlib.h>

long fib( int ); /* Fibonacci number function
prototype */

int main( int argc, char* argv[] )
{
int i;
i = atoi(argv[1]);
printf(“The Fibonacci number of %d = %ld\n”, i,
fib(i));
return 0;
}
We will not repeat the code for fib(i). A new header file,
stdlib.h, is included with this program. The function prototype
for atoi() is contained within this header file. The standard com­
mand line arguments are used in the call to main(). The line