Solution to question 11

#include <stdio.h>

int numOdds(int i, int j) {
  int tmp;

  // Swap i and j if necessary to ensure that i <= j.

  if (j < i) {
    tmp = i; i = j; j = tmp;
  }

  // Make i the largest odd number <= the original i.

  if (i % 2 == 0) i--;

  // Make j the smallest odd number >= the original j.

  if (j % 2 == 0) j++;

  // Allow for the special case that the original i and j were equal and odd.

  if (i == j) j += 2;

  // Finally, calculate the result.
  return (j - i)/2 - 1;
}

int main(void) {
  printf("%d %d %d\n", 3, 7, numOdds(3,7));
  printf("%d %d %d\n", 2, 4, numOdds(2,4));
  printf("%d %d %d\n", 4, 2, numOdds(4,2));
  printf("%d %d %d\n", 0,10, numOdds(0,10));
  printf("%d %d %d\n",-1, 0, numOdds(-1,0));
  printf("%d %d %d\n", 1, 1, numOdds(1,1));
  printf("%d %d %d\n", 1,-1, numOdds(1,-1));
  printf("%d %d %d\n", 1,-2, numOdds(1,-2));
  return 0;
}

Solution to question 12

#include <stdio.h>
#include <assert.h>

typedef struct {
    int hour;
    int minute;
    float second;
} time;

void addTimesAndPrint(time t1, time t2) {
  time t;

  // Verify that t1 and t2 are valid times.

  assert(t1.hour >= 0 &&
	 t1.hour < 24 &&
	 t1.minute >= 0 &&
	 t1.minute < 60 &&
	 t1.second >= 0.0F &&
	 t1.second < 60.0F);

  assert(t2.hour >= 0 &&
	 t2.hour < 24 &&
	 t2.minute >= 0 &&
	 t2.minute < 60 &&
	 t2.second >= 0.0F &&
	 t2.second < 60.0F);

  // Now add them, without worrying about overflow.

  t.hour   = t1.hour + t2.hour;
  t.minute = t1.minute + t2.minute;
  t.second = t1.second + t2.second;

  // Now correct for possible overflows.

  if (t.second >= 60.0F) {
    t.minute++;
    t.second -= 60.0F;
  }

  if (t.minute >= 60) {
    t.hour++;
    t.minute -= 60;
  }

  printf("%02d:%02d:%04.1f\n", t.hour, t.minute,t.second);
}


// A main program to test our function.
  
int main(void) {

  time t1 = {1, 30, 10.0};
  time t2 = {2, 30, 51.1};
  addTimesAndPrint(t1,t2);

  time t3 = {23, 59, 59.9};
  time t4 = {23, 59, 59.9};
  addTimesAndPrint(t3,t4);

  time t5 = {1, 30, 10.0};
  time t6 = {-1, 30, 61.0};
  addTimesAndPrint(t5,t6);

  return 0;
}

Solution to question 13

#include <stdio.h>

char *strcat(char *dest, char *src) {
  char *p;

  // Start at the first byte of the "dest" string.

  p = dest;

  // Increment our way through the string until we hit a
  // zero (i.e, the terminating null byte).

  while (*dest) {
    dest++;
  }

  // Now increment our way through the "src" string, until
  // we reach the end of it, copying bytes to "dest" as we go.

  while (*src) {
    *dest++ = *src++;
  }

  // Null-terminate the "dest" string.

  *dest = 0;

  // Return a pointer to the first byte of "dest".

  return p;
}

int main(void) {
  char dest[100] = "one";
  char src[] = "two";

  printf("the result is \"%s\"\n", strcat(dest, src));
  return 0;
}