C Programming Part 7: Pointers I

Topics

  • Basic pointer operations
  • Pointers to Arrays

Class Slides

Resources

Study Questions

  1. What value with the program print? 
    #include <stdio.h>
int main() {
  int x=4;
  int *y = &x;
  y++;
  printf("%d\n", *y);
}
  2. What value with the program print? 
     #include <stdio.h>
 int main() {
   int x = 4;
   int y = &x;
   y++;
   printf("%d\n", y++);
 }
  3. What value will the program print? 
     #include  <stdio.h>
 int main() {
   int x = 4;
   int* y = 5;
   y++;
   y++;
   printf("%d\n", y++);
 }
  4. What value will the program print? 
     #include <stdio.h>
 int main() {
   int x = 4;
   int* y = &x;
   (*y)++;
   printf("%d\n", y);
 }
  5. What value will the program print? 
     #include <stdio.h>
 int main() {
   int x = 4;
   int* y = &x;
   (*y)++;
   printf("%d\n", *y++);
 }
  6. The following programs are variations on the swap() program. See how the various changes to the code impact the results. What will this program print? 
     #include <stdio.h>

 void swap(int a, int b) {
   int temp = a;
   a = b;
   b = temp;
 }

 int main() {
   int x = 10, y = 20;
   swap(x, y);
   printf("%d\n", x);
 }
  7. What will this program print? 
     #include <stdio.h> 

 void swap(int *a, int *b) {
   int temp = a;
   a = b;
   b = temp;
 }

 int main() {
   int x = 10, y = 20;
   swap(x, y);
   printf("%d\n", x);
 }
  8. What will this program print? 
     #include <stdio.h>

 void swap(int *a, int *b) {
   int temp = a;
   *a = b;
   b = temp;
 }

 int main() {
   int x = 10, y = 20;
   swap(&x, &y);
   printf("%d\n", x);
 }
  9. What will this program print (note that it is printing y)? 
     #include <stdio.h>

 void swap(int *a, int *b) {
   int* temp = a;
   *a = *b;
   *b = temp;
 }

 int main() {
   int x = 10, y = 20;
   swap(&x, &y);
   printf("%d\n", y);
 }
  10. What will this program print (note that it is printing y)? 
     #include <stdio.h>

 void swap(int *a, int *b) {
   int temp = a;
   *a = *b;
   *b = temp;
 }

 int main() {
   int x = 10, y = 20;
   swap(&x, &y);
   printf("%d\n", y);
 }
  11. What will this program print (note that it is printing y)? 
     #include <stdio.h>

 void swap(int *a, int *b) {
   int temp = *a;
   *a = *b;
   *b = temp;
 }

 int main() {
   int x = 10, y = 20;
   swap(&x, &y);
   printf("%d\n", y);
 }
  12. (T or F) The program below will generate an error or warning when compiled. 
     #include <stdio.h>
 #define SIZE 20
 int main() {
   char str[SIZE] = "hi there!\n";
   char* strp = str;
 }
  13. What will this program print? 
    #include <stdio.h>
#define SIZE 20
int main() {
  char str[SIZE] = "hi-there!\n";
  char* strp = &str[8];
  printf("%c\n", strp);
}
  14. What will this program print? 
     #include <stdio.h>
 #define SIZE 20
 int main() {
   char str[SIZE] = "hi-there!\n";
   char* strp = &str[7];
   printf("%c\n", *(strp+1));
 }
  15. What will this program print? 
     #include <stdio.h>
 #define SIZE 20
 int main() {
   char str[SIZE] = "hi-there!\n";
   char* strp = &str[1];
   printf("%c\n", *(strp++));
 }
  16. What will this program print? 
     #include <stdio.h>
 #define SIZE 20
 int main() {
   char str[SIZE] = "hi-there!\n";
   char* strp = str;
   printf("%c\n", *(++strp));
 }
  17. (T or F) This program will compile correctly. 
     #include <stdio.h>
 #define SIZE 20
 int main() {
   char str[SIZE] = "hi-there!\n";
   char* strp = str++;
   printf("%c\n", *strp);
 }
  18. What does this program print? 
     #include <stdio.h>

 void mystery(char a[]) {
   a[1] = 'b';
 }

 #define SIZE 20
 int main() {
   char str[SIZE] = "hi-there!\n";
   mystery(str);
   printf("%c\n", str[1]); 
 }
  19. What does this program print? 
     #include <stdio.h>
 void mystery(char a[]) {
   *(a+1) = 'b';
 }

 #define SIZE 20
 int main() {
   char str[SIZE] = "hi-there!\n";
   mystery(str);
   printf("%c\n", str[1]); 
 }
  20. What does this program print? 
     #include <stdio.h>
 void mystery(char* a) {
   *(a+1) = 'b';
 }

 #define SIZE 20
 int main() {
   char str[SIZE] = "hi-there!\n";
   mystery(str);
   printf("%c\n", str[1]); 
 }
  21. What does this program print? 
     #include <stdio.h>
 void mystery(char a[]) {
   *(a++) = 'b';
 }
    
 #define SIZE 20
 int main() {
   char str[SIZE] = "hi-there!\n";
   mystery(str);
   printf("%c\n", str[1]); 
 }
  22. What will this program print? Is the result implementation-independent? 
     #include <stdio.h>
    
 int main() {
   int* x = 4;
   printf("%d\n", ++x);
 }
  23. Write a function that takes an array of ints (nums) and returns a pointer to the largest element. Create a test program that calls the function and prints out the largest value.
  24. Write a function that takes a string (str) and int (i), and prints the string from location i to the end.
  25. Write a function that takes a string (str) and a pointer to a location in the string (p), and prints everything up to, but not including the character pointed to by p. Create a test program that calls this function.
  26. Write a function that increments an int from the caller function. Create a test program that calls this function and prints the modified int before and after calling the function.
  27. Write a function swap that swaps two char variables from the caller function. Create a test program that calls this function and prints the chars before and after calling swap.
  28. Write a function reverse that uses your swap function from the previous question to reverse the direction of the string. Create a test program that prints a string before and after using the reverse function.
  29. Write a function replicate that takes a string and prints it out twice consecuitively to a provided location. Create a test program that prints the new string.