This week your tutor will show you how it is to be done in future weeks.

Your tutor will nominate a lab pair this week to do next week's code review.

How a code review works:

• The reviewees show their code on the projector, and briefly walk through how it works.
• The class and tutor (the reviewers) give feedback, ask questions, make suggestions. You tutor will show you how to do this at first but then will expect the other reviewers to take over.
• Reviewers are NOT negative, a review is to be supportive and constructive and helpful to the reviewees.
• The reviewees should speak very little, just give a brief overview of the code they want reviewed.
• Let everyone have a turn to speak, don’t dominate the conversation.
• Contribute and participate, don’t be silent. If you don’t understand anything then that doesn’t mean be silent - it means ASK for an explanation. By asking you are helping the coders to see how to be clearer.

If they are valid, would they be a good name?

• THX1138 Valid, not good - doesn't start with a lower-case letter
• 2for1 Invalid - doesn't start with a letter or underscore
• mr_bean Valid, good if the variable has something to do with Mr Bean
• my space Invalid - you can't have spaces in variables names
• event_counter Valid in C, good
• ^oo^ Invalid - only letters, numbers and underscore allowed
• _MEMLIMIT Valid not good - doesn't start with a lower-case letter
• return Invalid - this is a special keyword in C

C is a typed language. What does this mean? Why is this useful?

Reminder: there 2.54 centimetres in an inch and 12 inches in a foot.

Use only int variables.

Your program should behave like this:

./cm2feet
Enter your height in centimetres: 183
Your height in feet is 6

// Author: anonymous
// Date created: ?
// Convert height from centimetres to feet.

#include <stdio.h>

#define INCHES_IN_FOOT  12
#define CM_IN_INCH      2.54

int main (void) {
    int height_centimetres;
    int height_feet;

    printf("Enter your height in centimetres: ");
    scanf("%d", &height_centimetres);

    height_feet = (height_centimetres / CM_IN_INCH) / INCHES_IN_FOOT;

    printf("Your height in feet is %d\n", height_feet);

    return 0;
}

Would double variables have been a better choice?

dcc -o count42 count42.c
./count42
1
2
3

// Print the integers 1..42, one per line.
// COMP1511 tutorial example
// Andrew Taylor - andrewt@unsw.edu.au

#include <stdio.h>

int main(void) {
    int i;
    
    i = 1;
    while (i <= 42) {
        printf("%d\n", i);
        i = i + 1;
    }
    
    return 0;
}

dcc -o count_up count_up.c
./count_up
Enter finish: 3
1
2
3
./count_up
Enter finish: 7
1
2
3
4
5
6
7

// Print the integers 1..n, one per line.
// COMP1511 tutorial example
// Andrew Taylor - andrewt@unsw.edu.au
// 25/3/2018

#include <stdio.h>

int main(void) {
    int i, finish;
    
    printf("Enter finish: ");
    scanf("%d", &finish);
    
    i = 1;
    while (i <= finish) {
        printf("%d\n", i);
        i = i + 1;
    }
    
    return 0;
}

dcc -o range range.c
./range
Enter start: 3
Enter finish: 7
3
4
5
6
7

// Print the integer n..m one per line
// COMP1511 tutorial example
// Andrew Taylor - andrewt@unsw.edu.au

#include <stdio.h>

int main(void) {
    int i, start, finish;
    
    printf("Enter start: ");
    scanf("%d", &start);
    
    printf("Enter finish: ");
    scanf("%d", &finish);
    
    i = start;
    while (i <= finish) {
        printf("%d\n", i);
        i = i + 1;
    }
    
    return 0;
}

Hint: if x is divisible by 7, then x % 7 == 0

dcc -o range7 range7.c
./range7
Enter start: 3
Enter finish: 49
7
14
21
28
35
42
49

// Print multiples of 7 between two numbers
// COMP1511 tutorial example
// Andrew Taylor - andrewt@unsw.edu.au

#include <stdio.h>

int main(void) {
    int i, start, finish;
    
    printf("Enter start: ");
    scanf("%d", &start);
    
    printf("Enter finish: ");
    scanf("%d", &finish);
    
    i = start;
    while (i <= finish) {
        if (i % 7 == 0) {
            printf("%d\n", i);
        }
        i = i + 1;
    }
    
    return 0;
}

dcc -o range_divisible range_divisible.c
./range_divisible
Enter start: 20
Enter finish: 100
Enter divisor: 13
26
39
52
65
78
91
./range_divisible
Enter start: 80
Enter finish: 120
Enter divisor: 5
80
85
90
95
100
105
110
115
120

// Print multiples of given number between two numbers
// COMP1511 tutorial example
// Andrew Taylor - andrewt@unsw.edu.au

#include <stdio.h>

int main(void) {
    int i, start, finish, divisor;
    
    printf("Enter start: ");
    scanf("%d", &start);
    
    printf("Enter finish: ");
    scanf("%d", &finish);
    
    printf("Enter divisor: ");
    scanf("%d", &divisor);
    
    i = start;
    while (i <= finish) {
        if (i % divisor == 0) {
            printf("%d\n", i);
        }
        i = i + 1;
    }
    
    return 0;
}

Revision questions

Your tutor may still choose to cover some of the questions time permitting.

./rectangle_area
Please enter rectangle length: 3.14159
Please enter rectangle width: 2.71828
Area = 8.539721

// Compute area of a rectangle using doubles
// Modified 3/3/2017 by Andrew Taylor (andrewt@unsw.edu.au)
// as a lab example for COMP1511

// Note this program doesn't check whether
// the two scanf calls successfully read a number.
// This is covered later in the course.

#include <stdio.h>

int main(void) {
    double length, width, area;

    printf("Please enter rectangle length: ");
    scanf("%lf", &length);
    printf("Please enter rectangle width: ");
    scanf("%lf", &width);

    area = length * width;

    printf("Area = %lf\n", area);

    return 0;
}

What is output by the following C program? Why? Make sure you compile the program and run it to confirm your answer.

#include <stdio.h>

#define FIRST_NUMBER     10
#define SECOND_NUMBER    20
#define TOTAL   FIRST_NUMBER + SECOND_NUMBER
#define AVERAGE TOTAL / 2

int main(void) {
    printf("The average of %d and %d is %d\n",
           FIRST_NUMBER, SECOND_NUMBER, AVERAGE);

    return 0;
}

#include <stdio.h>

#define FIRST_NUMBER     10
#define SECOND_NUMBER    20
#define TOTAL   (FIRST_NUMBER + SECOND_NUMBER)
#define AVERAGE (TOTAL / 2)

int main(void) {
    printf("The average of %d and %d is %d\n",
           FIRST_NUMBER, SECOND_NUMBER, AVERAGE);

    return 0;
}

Determine the value of each expression and sub-expression:

1. 1 / 2 * 500
   1 / 2 = 0; 0 * 500 = 0
2. 1 / 2.0 * 500
   1/2.0 = 0.5; 0.5 * 500 = 250.0
3. (17 / 5) * 5 + (17 % 5)
   17 / 5 = 3; 17 % 5 = 2; 3 * 5 = 15; 15 + 2 = 17
4. (12 - 17) % 6 - 4
   
   12 - 17 = -5; -5 % 6 = -5; -5 - 4 = -9

Your program should behave as follows:

./decompose
Please enter an integer: 25
You entered 25 which is decomposed: 2 5
./decompose
Please enter an integer: 2825
You entered 2825 which is decomposed: 2 8 2 5
./decompose
Please enter an integer: 2
You entered 2 which is decomposed: 2

Your program should handle all integers in range (0 to 99999).

Hint: use if, divide (/) and mod (%).

#include <stdio.h>

int main(void) {
    int val, orig_val;
    printf("Please enter an integer: ");
    scanf("%d", &val);

    printf("You entered %d which is decomposed:", val);
    orig_val = val;

    if (orig_val > 9999) {
        printf(" %d", val / 10000);
        val = val % 10000;
    }
    if (orig_val > 999) {
        printf(" %d", val / 1000);
        val = val % 1000;
    }
    if (orig_val > 99) {
        printf(" %d", val / 100);
        val = val % 100;
    }
    if (orig_val > 9) {
        printf(" %d", val / 10);
        val = val % 10;
    }
    printf(" %d\n", val);

    return 0;
}

#include <stdio.h>

int main(void) {
    int input;
    printf("Please enter an integer: ");
    scanf("%d", &input);
    printf("You entered %d which is decomposed:", input);

    if (input <= 0) {
        // edge case
        printf(" %d", input);
    } else {
        int divisor = 10000; // can generalize this
        int in_number = 0;
        while (divisor != 0) {
            if (input / divisor != 0) {
                // avoid leading zeroes
                in_number = 1;
            }
            if (in_number) {
                printf(" %d", input / divisor);
            }
            input %= divisor;
            divisor /= 10;
        }
    }

    printf("\n");
    return 0;
}

Discuss the concept of short-circuit evaluation for the C logical operators || and &&. Give examples. Why is this feature useful?