COMP1721 - Higher Computing 1B

1. No. Indenting and other formatting is vital for humans reading C program but it is not required by the compiler.

2. • Anything that is between /* and */ is interpreted as a comment by the compiler. [true]
   • Everything after -- on a line is treated as a comment. [false]
   • Variables must always be declared before they are used. [true]
   • A compound statement (a list of statements enclosed in curly braces {}) can be placed anywhere in a program where a single statements. [true]

3. This C:

   ---

   /* The meaning of life is:
   printf("%d\n", 6*7);
   
   
   

   ---

   is incorrect and does not compile:

   ---

   example.c:1:35: unterminated comment
   example.c: In function `main':
   example.c:1: error: syntax error at end of input
   

   ---

4. • forty is legal
   • forty_two is legal
   • forty two is not legal, spaces can not appear in variable names
   • forty#two is not legal, #s can not appear in variable names
   • 42 is not legal, a variable name can not start with a digit
   • f42 is legal
   • while is not legal, while is a reserved word in C

5. This C:

   ---

   
   answer = 42;
   printf("%d\n", answer);
   

   ---

   is incorrect and does not compile:

   ---

   example.c: In function `main':
   example.c:2: error: `answer' undeclared (first use in this function)
   example.c:2: error: (Each undeclared identifier is reported only once
   example.c:2: error: for each function it appears in.)
   

   ---

   All variables must be declared before they are used.

6. This C:

   ---

   int x, y;
   x = 15;
   y = x;
   x = 27;
   printf("%d\n", y);
   

   ---

   produces this output:

   ---

   15
   

   ---

   The assignment y = x assigns the current value of x to y. It is not a declaration of equality. C is not Haskell!

7. This C:

   ---

   int x;
   x = "hello world";
   printf("%d\n", x);
   

   ---

   is incorrect and does not compile:

   ---

   example.c: In function `main':
   example.c:2: warning: assignment makes integer from pointer without a cast
   example.c: In function `main':
   example.c:2: warning: assignment makes integer from pointer without a cast
   

   ---

   Only values of the appropriate type can be assigned to a variable.

8. This C:

   ---

   int x;
   x = 42;
   printf("%d\n", X);
   

   ---

   is incorrect and does not compile:

   ---

   example.c: In function `main':
   example.c:3: error: `X' undeclared (first use in this function)
   example.c:3: error: (Each undeclared identifier is reported only once
   example.c:3: error: for each function it appears in.)
   

   ---

   Case is significant in C variable names.

9. #include <stdio.h>
   
   int
   main(void) {
       int n1, n2, product;
    
       printf("Enter first number: ");
       scanf("%d", &n1);
       printf("Enter second number: ");
       scanf("%d", &n2);
       product = n1 * n2;
       printf("The product of %d and %d is %d\n", n1, n2, product);
       return 0;
   }
   

10. The design for the program follows the idea ...

    	write a loop to iterate 100 times
    	in each iteration of the loop
    		print the message
    

        int i;
    	
        i = 0;
        while (i < 100) {
            printf("I must not talk during lectures\n");
            i = i + 1;        
        }
       

11. A simple Haskell solution is

    sigma n m
     | n > m      = 0
     | otherwise  = n + sigma (n + 1) m
    

    another Haskell solution is

    sigma n m = sum [n..m]
    

    These C statements will print the sum of the numbers n to m:

    
            int number;
            int total;
    
            total = 0;
            number = n;
    
            while (number <= m) {
                total = total + number;
                number = number + 1;
            }
            
            printf("%d\n", total);
    

12. A suitable Haskell function is:

    sigma n m
     | n > m      = 0
     | otherwise  = n + sigma (n + 1) m
    
    tetrahedral n
     | n == 1    = 1
     | n > 1     = (sigma 1 n) + (tetrahedral (n - 1))
     | otherwise  = error "tetrahedral: illegal argument"
    

    These C statements will print the first 100 tetrahedral numbers:

            int i,j, n, total;
    		
            n = 1;
    
            while (n <= 100) {
                total = 0;
                j = 1;
                
                
                while (j <= n) {
                	i = 1;
                	while (i <= j) {
                    	total = total + i;
                   	    i = i + 1;
                   	}
                   	j = j + 1;
                }
                printf("%d\n", total);
                n = n + 1;
            }