Then we changed types of the variables: instead of int we made them double and changed the format specifiers correspondingly: from %d to %lf. The result of division 8/3 in the last line has changed: it was 2 for int and it became 2.666666 for double.

We also checked what happens if a variable of type double was printed with format specifier %d (as though it was an integer), see printf("After z=2*x-y... The result didn't look meaningful.

/******************************* 
 File lab3.c
 M2120-Fall'05-Lab 3- Thursday 
 Author: Sergey Sadov 
 Date: Thursday Sept.22 2005 
 Program from Wed Sept 21 Lecture
********************************/

#include <stdio.h>

int main()
{
  double x; 
  double y;
  double z;

  printf("Before initialization: x=%lf, y=%lf, z=%lf\n",x,y,z);
  x=2;
  printf("After x=2: x=%lf, y=%lf, z=%lf\n",x,y,z);
  y=5;
  printf("After y=5: x=%lf, y=%lf, z=%lf\n",x,y,z);
  x=x+5;
  printf("After x=x+5: x=%lf, y=%lf, z=%lf\n",x,y,z);
  y++;
  printf("After y++: x=%lf, y=%lf, z=%lf\n",x,y,z);
  z=2*x-y;
  printf("After z=2*x-y: x=%d, y=%d, z=%d\n",x,y,z);
  y/=2;
  printf("After y/=2: x=%lf, y=%lf, z=%lf\n",x,y,z);
  z=z/y;
  printf("After z=z/y: x=%lf, y=%lf, z=%lf\n",x,y,z);
  printf("Done\n");
  
  return(0);
}

Second half of the lab: Next program demonstrates some useful mathematical functions and the pi (M_PI) constant.
To compile a program that contains #include<math.h> the option -lm ("Load Math") is required in the command line:
     gcc -lm lab3b.c

/******************************* 
 File lab3b.c
 M2120-Fall'05-Lab 3- Thursday 
 Author: Sergey Sadov 
 Date: Thursday Sept.22 2005 
 Math functions in C
********************************/

#include<stdio.h>
#include<math.h>  /* Necessary, to provide an access to math functions */

int main()
{
  double x; 
  double y;
  double z;

  x=0.0; y=0.0; z=0.0;
  printf("After initialization: x=%lf, y=%lf, z=%lf\n",x,y,z);
  
  /* In the following fragment we want to find sin(90 degrees) and print 
the result */
  x=90.0;
  z=x*(M_PI/180.0); /*multiplying by conversion factor from degrees to 
radians */
  y=sin(z); /* sin,cos,tan functions in C work with radian measure */
  printf("sin(%lf)=%lf\n",x,y);
  
 /* Next fragment features the "power" function pow. We compute 2 to the 
power 3 and print result */
  x=3.0;
  y=2.0;
  z=pow(y,x);
  printf("%lf^%lf=%lf\n",y,x,z);

/* To find e to the power x, there is a more efficient method: 
as an example we print e squared */ 

  x=2.0;
  y=exp(x);
  printf("e^%lf=%lf\n",x,y);

  printf("Done\n");
  
  return(0);
}