COMP 1917 Computing 1
Session 2, 2016

Tutorial Solutions - Week 2

1. Introduce yourselves, get to know your tutor - how can you contact them?

2. State briefly what each of the following Unix commands does:
   • mkdir
         "make directory" (create a new directory or "folder")
   • cd
         "change directory"
   • pwd
         "print working directory" (print the full path of the current directory)
   • ls
         "list" the files (and subdirectories) in the current directory
   • cp
         "copy" a file
   • mv
         "move" a file (i.e. change its name)
   • rm
         "remove" (i.e. delete) a file
   • rmdir
         "remove directory"
   • man
         on-line "manual"; for example, to find out about the "diff" command, you would type:
         man diff
     
   • passwd
         change your password

3. Which of the following are valid variable names in C? Which are not?

   • THX1138: valid
   • 2for1: invalid (begins with a digit)
   • MrBean: valid
   • My Space: invalid (contains a space)
   • still_counting: valid
   • ^oo^: invalid (contains punctuation)
   • _MEMLIMIT: valid, but discouraged (begins with underscore)

4. Write a C program which allows the user to enter a number and then prints the square root of that number, to two decimal places.

     #include <stdio.h>
     #include <math.h>
   
     int main( void )
     {
       float x;
   
       printf("Enter a number: " );
       scanf( "%f", &x );
       printf("The square root of %1.2f is %1.2f\n", x, sqrt(x));
   
       return 0;
     }
   

5. How would you modify your program so it computes the cube root instead of the square root? (Hint: use the pow() function, described here).

   replace sqrt(x) with pow( x, 1.0/3.0)

6. Suppose you have written a C program and saved it to a file heron.c. What would you type on the UNIX command line to compile this program, producing the object file heron ? How would you then run this program?

      gcc -Wall -o heron heron.c
   

7. Write a program which inputs the sidelengths a, b and c of a triangle, and computes the area of the triangle using Heron's formula:

      area = sqrt(s(s-a)(s-b)(s-c))
   

   where s is the "semi-perimeter"

      s = (a + b + c)/2.
   

     /*
        heron.c
   
        Use Heron's formula to compute the area of a triangle,
        given the side lengths.
     */
   
     #include <stdio.h>
     #include <math.h>
     // remember to compile with -lm
   
     int main( void )
     {
       float a,b,c; // sidelengths of a triangle
       float s;     // semi-perimeter
       float area;
   
       printf( "Enter sidelengths of a triangle:\n" );
   
       scanf( "%f", &a );
       scanf( "%f", &b );
       scanf( "%f", &c );
   
       // compute semi-perimeter
       s = ( a + b + c )/ 2;
   
       // compute area using Heron's formula
       area = sqrt(s*(s-a)*(s-b)*(s-c));
   
       printf( "Area = %1.2f\n", area );
   
       return 0;
     }