Question

Ensure the following compiles

5. Variable scope (1 mark)

Some variables are only accessible while executing specific code. Global variables are often thought of as evil because the state of a system can be altered making functions execute differently when it isn't expected.

There is also the issue of block scope. For an example of block scope, see the file below. Notice that you don't get an error because the code uses the correct syntax. Although the syntax is correct, you cannot access the variable "val" outside of the if/else statement. So any time you intend to use a variable, it can only accessed in code blocks nested deeper than the block it was declared in. It's generally good practice to use variables in the deepest block you can so variables aren't confused or unintentionally altered.

%%file src/scope.c

/***
* Name:
* Date:
* Course:
*
* Description:
***/

#include <stdio.h>

/* Returns 1 if num is positive (> 0), 0 if num is negative or 0*/
int isPositive(int num) {
    int val;
    
    if(num > 0) {
        int val = 1;
    } else {
        int val = 0;
    }
    
    return val;
}



int main() {
    
    printf("%d\n", isPositive(6));
    printf("%d\n", isPositive(-6));
    
    return 0;
}


%%bash
gcc src/scope.c -o bin/testScope
./bin/testScope

Now that you have seen a runtime bug slip through the cracks, try adding the flags we normally use in this course to the code above to see what happens.

5.a. Fix the code below (1 mark)

Fix the code below to properly display the result. The program contains a single block of code around the if/else statement. You can change the code however you want to display the correct result as long you don't change the function signature. i.e. parameters and return value

Don't code like this, it's very difficult to read and predict behaviour because programmers easily confuse which variable is being accessed, thus varying the expected behaviour. This is just to demonstrate what you should avoid and why this is undesirable.

%%file src/scope.c

/***
* Name:
* Date:
* Course:
*
* Description:
***/

#include <stdio.h>


/* Global variable, avoid using these! */
int num = 6;


/* Returns 1 if num is positive (> 0), 0 if num is negative or 0*/
int isPositive(int num) {
    int val;
    
    {
        extern int num;
        
        if(num > 0) {
            int val = 1;
        } else {
            int val = 0;
        }
    }
    
    return val;
}


%%file include/lab2.h

/***
* Name:
* Date:
* Course:
*
* Description:
***/


#include<stdio.h>


/***
* Function prototype
***/


/* ifElse.c */
int newNumber(int oldNumber);


/* switch.c files */
int replaceZero(int numTwo);

int userDecision(int userInput, int numOne, int numTwo);


/* while.c */
int absoluteValue(int value);

int overflow(int dividend, int divisor);


/* forLoop.c */
float average(float numbers[], int length);


/* scope.c */
int isPositive(int num);



%%file src/main.c

/***
* Name:
* Date:
* Course:
*
* Description:
***/


#include "lab2.h"

int main(int argc, char *argv[]) {
    /* average is 6.0 */
    float aTestOne[] = {5.0, 6.0, 7.0};
    
    printf("Hello, World\n");
    
    printf("\n*** If/else ***\n");
    printf("This should be 1, %d\n", newNumber(0));
    printf("This should be 21, %d\n", newNumber(-21));
    printf("This should be 0, %d\n", newNumber(21));
    printf("This should be 13, %d\n", newNumber(13));
    
    printf("\n*** switch ***\n");
    
    printf("\n*** while loop ***\n");
    printf("overflow of 25/6 = %d, (should be %d)\n", overflow(25, 6), 5);
    printf("overflow of -14/9 = %d, (should be %d)\n", overflow(-14, 9), 4);
    
    printf("\n*** for loop ***\n");
    
    printf("\n*** Variable scope ***\n");
    
    return 0;
}

%%bash
gcc src/scope.c -o bin/testScope
./bin/testScope

6.b. Pass by Reference (2 marks)

Pass by reference refers to how variables are passed in functions when using pointers in c. Pointers behave differently (pass by reference) unlike pass by value shown above, finish the code below to swap the value of two char* variables passed. This can be a little difficult when first learning the basics of programming, but stick with it and pointer manipulation will eventually make sense.

%%file src/swap.c

/***
* Name:
* Date:
* Course:
*
* Description:
***/

void swapString(char **varOne, char **varTwo) {
    
}

%%file include/lab2.h

/***
* Name:
* Date:
* Course:
*
* Description:
***/


#include<stdio.h>


/***
* Function prototypes
***/


/* from ifElse.c */
int newNumber(int oldNumber);


/* switch.c files */
int replaceZero(int numTwo);

int userDecision(int userInput, int numOne, int numTwo);


/* while.c */
int absoluteValue(int value);

int overflow(int dividend, int divisor);


/* forLoop.c */
float average(float numbers[], int length);


/* scope.c */
int isPositive(int num);


/* swap.c */
void swapString(char **varOne, char **varTwo);

%%file src/main.c
/***
* Name:
* Date:
* Course:
*
* Description:
***/


#include "lab2.h"


int main(int argc, char *argv[]) {
    char *stringOne = "String one!";
    char *stringTwo = "String, the second!";
    
    printf("Hello, World\n");
    
    printf("\n*** If/else ***\n");
    printf("This should be 1, %d\n", newNumber(0));
    printf("This should be 21, %d\n", newNumber(-21));
    printf("This should be 0, %d\n", newNumber(21));
    printf("This should be 13, %d\n", newNumber(13));
    
    printf("\n*** switch ***\n");
    
    printf("\n*** while loop ***\n");
    printf("overflow of 25/6 = %d, (should be %d)\n", overflow(25, 6), 5);
    printf("overflow of -14/9 = %d, (should be %d)\n", overflow(-14, 9), 4);
    
    printf("\n*** for loop ***\n");
    
    printf("\n*** Variable scope ***\n");
    
    printf("\n*** swap ***\n");
    printf("swap \"%s\" with \"%s\"\n", stringOne, stringTwo);
    swapString(&stringOne, &stringTwo);
    printf(" stringOne = \"%s\" \n", stringOne);
    printf(" stringTwo =\"%s\" \n", stringTwo);
    
    return 0;
}


I'm being lazy after compiling this many times. I am going to shorten everything by compiling all the c files in the src directory into a single exexutable using the "src/*.c" command to select all of the files. Before doing this you need to be sure that there is only one main function defined or the compiler will not be able to choose which main function to run.

%%bash
gcc -Wall -pedantic -ansi -Iinclude src/*.c -o bin/runMe
./bin/runMe

Answer 1

Please find my implementation for two function.

Please repost others in sepatate post.

/*For loops are used when the developer knows the number of iterations.
Write a for loop to find the average of a list of floats, use the skeleton below
and make sure to return a float.*/

/***
* Name:
* Date:
* Course:
*
* Description:
***/

float average(float numbers[], int length) {
float sum = 0;
int i;
for(i=0; i<length; i++)
sum = sum + numbers[i]

return sum/length;
}

// 6.b
void swapString(char **varOne, char **varTwo) {

char *t = *varOne;
*varOne = *varTwo;
*varTwo = t;
}