Quiz 4

• Answer

  preprocessing

• Answer

  #define FUN_DIVIDE((a), (b)) (((a) / (b)) + 9.0)

  Necessary to include parenthesis around each 'parameter' (recall macro perils).

#include "foo1.h"

	static double PI = 3.1415;
	
	int void main() {
	
		printf("Hello Quiz 4");

	}

Is this valid? Why or why not?

• Answer

  INVALID

  main() is a function defined to have a return type of both int AND void, which is invalid

#include <stdio.h>
	int *getNthElement(int n) {
		static int nums[] = {48, 45, 69, 02, 12, 61, 04, 58, 42, 82};
		char letter = 'U';
		int myNum = nums[n];
		return &myNum;
	}
	
	int count = 8348;

	int main(void) {
		int *x = getNthElement(6);
		printf("%d\n", *x);
		return 0;
	}

getNthElement

nums

count

x

n

• Answer

  getNthElement: data segment

  nums: data segment

  count: data segment

  x: stack

  n: stack

a) b is a pointer to a pointer to a long

b) f is a pointer to a function that takes in a pointer to an int and returns a pointer to a pointer to a char

c) junk is a pointer to a function that takes in no parameters and returns a pointer to a pointer to a struct trash

d) h is an array of size 2110 that contains pointers to pointers to struct students

• Answer

  1. long **b

  2. char **(*f)(*int);

  3. struct trash **(*junk)(void)

  4. struct student **h[2110]

#include <stdio.h>

void func(int a, int *b, int *c) {
	a++;
	c = b;
	*b = a + 7;
	(*c)++;
}

void main(void) {
	int a = 12;
	int b = 9;
	int c = 36;
	func(a, &b, &c);
	printf("a: %d\n", a);
	printf("b: %d\n", b);
	printf("c: %d\n", c);
}

a:

b:

c:

Which of the arguments are passed by reference?

• Answer:

  a: 12

  b: 21 ( 12 + 7 + 1)

  c: 36

  Which of the arguments are passed by reference? None

  

#include <stdio.h>

char * returnSomeLetters(char *str) {
	char result[4];
	for (int i = 0; i < 3; i++) {
		result[i] = str[i];
	}
	result[3] = '\0';
	return result;
}

int main() {
	char string[] = "cs2110 is my favorite class";
	char *result = returnSomeLetters(string);
	printf("%s", result);
}

• Answer

  The code fails. The result is declared on the stack since it exists inside the function. When it is returned, the address of the result cannot be found since the stack is reset, and the pointer to the result will go somewhere bad.

struct Doggo {
	char * name;
	int goodBoi;
	long numMailmenScared;
	int isChonker;
};

int isVeryGoodBoi() {
	if (newDoggo->isChonker) {
		return 1;
	}
	if (newDoggo->numMailmenScared <= 0) {
		return 0;
	}
	if (newDoggo->goodBoi) {
		return 1;
	} else {
		return 0;
	}
}

• Answer

  The answer is that newDoggo could be an invalid pointer such as NULL, if so, dereferencing it would cause a seg fault.

char * OH = "By Appointment Only";

char arr[20] = "1 to 3";

char * temp = arr;

arr = OH; //line 4

OH = temp; //line 5

• Answer

  line 4 is not valid since we cannot assign thee string OH to the array arr;

#include <stdio.h>
#include <string.h>

//stats struct
struct stats {
	int age;
	double barkPower;
	double jumpHeight;
}

//puppy struct
struct puppy {
	char *name;
	struct stats puppyStats;
}

int main() {
	struct puppy p1;
	doublePower(&p1);
	return 0;
}

int doublePower(//CODE HERE) {
	//CODE HERE
}

• Answer

  int doublePower(struct puppy *p) {
  	p->puppyStats.barkPower = (p->puppyStats.barkPower) * 2;
  }

You may assume long is 8 bytes, an int is 4 bytes, a short is 2 bytes, and a char is 1 byte.

int * ptr1 = (int*)(0x123013);

short * ptr2 = (short*)(0x123008);

long* ptr3 = (long*)(0x123000);

Answer the following questions. Give your answer in hexadecimal.

ptr3 = ?

ptr3 + 1 = ?

*(ptr1 + 2) = ?

*(ptr2 +4) = ?

• Answer

  ptr3 = 0x123000

  ptr3 + 1 = 0x123008

  *(ptr1 + 2) = 0xC2D4E3A1. 123013 + 2*4 = 12301B

  *(ptr2 + 4) = 0xDB8E. 123008 + 8 = 123010

• strncmp

• strncpy

• strlen

You can assume string.h has already been included.

Write a function replaceCharWithString that replaces a char with string. Do NOT modify the original string. You will be given 4 arguments:

• (char *originalString). null-terminated string to modify.

• (char charToReplace). char you are looking to replace

• (char *stringReplace). null-terminated string that will replace the char

• (char *result). string to store the result. You can assume that it has been initialized with enough memory to hold the entire resulting null-terminated string.

Example 1: replaceCharWithString("hi", 'i', "ello", res) should result in res containing the null-terminated string "hello".

Example 2: replaceCharWithString("beautiful", 'u', "uwu", res) should result in res containing the null-terminated string "beauwutifuwul".

Copy the following function header into the box:

void replaceCharWithString(char * originalString, char charToReplace, char * stringReplace, char *result)

• Answer

  void replaceCharWithString(char *originalString, char charToReplace, char *stringReplace, char *result) {
      const int replaceLen = strlen(stringReplace);
      while (*originalString) { // until we reach a null terminator
          if (*originalString == charToReplace) {
              strncpy(result, stringReplace, replaceLen); // copy all replacement chars except the null terminator
              result += replaceLen;
          } else {
              *result = *originalString; // copy the current character
              result++;
          }
          originalString++; // look at the next character
      }
      *result = '\0'; // ensure the result is null-terminated
  }