125: Mainline

In the following program, for example, r's value is 5.0 before doubling_time has been entered, r's value is 10.0 as doubling_time is executed, and r's value is 5.0 after the execution of doubling_time.

#include  
#include  
/* Define doubling_time first */ 
double doubling_time (double r) { 
  return log (2.0) / log (1.0 + r / 100.0); 
} 
/* Then, define main */ 
main ( ) { 
  double r = 5.0; 
  printf ("The value of r is %f.\n", r); 
  printf ("The doubling time at twice that rate is %f.\n", 
          doubling_time (r + r)); 
  printf ("The value of r is still %f.\n", r); 
} 
--- Result --- 
The value of r is 5.000000. 
The doubling time at twice that rate is 7.272541. 
The value of r is still 5.000000.