Week 03 Tutorial Sample Answers

Tutorial Overview:

Part 1: While Loops (15 mins)

In the lectures we have seen 3 types of loops: count, sentinel and conditional.

In this activity your tutor will run through the structure of a while loop, hand-execute a loop and then will convert to a flowchart to working C code.

Tutor demo (8 mins)

The structure of a while loop

while (/* some condition is true */) {
    // loop body
    // execute some code
}

// rest of program

structure of a while loop diagram

Programming a while loop

Convert the following flowchart to C code and hand execute the program.

example while loop diagram

Your Turn! (7 mins)

In groups of 3-4 hand execute the following loops writing down what would be output to the terminal:

A 
#include <stdio.h>

int main(void) {
    int i = 0;
    while (i < 32) {
        printf("%d\n", i);
        i = i + 2;
    }
	return 0;
}
B 
#include <stdio.h>

int main(void) {
    int i = 5;
    while (i >= 0) {
        printf("%d\n", i);
        i--;
    }
	return 0;
}
C 
#include <stdio.h>

int main(void) {
    int i = 0;
    int keep_going = 1;
    while (keep_going == 1) {
        if (i > 3) {
            keep_going = 0;
        }
        i++;
    }
    printf("%d\n", i);
	return 0;
}
D 
#include <stdio.h>

int main(void) {
    int i;
    while (i > 0) {
        printf("%d\n", i);
        i--;
    }
	return 0;
}
E 
#include <stdio.h>

int main(void) {
    int i = 0;
    int max = 32;
    while (i < max) {
        printf("%d\n", i);
        max = max + 2;
    }
	return 0;
}
F 
#include <stdio.h>

int main(void) {
    int i = 0;
    int keep_going = 0;
    while (keep_going == 1) {
        if (i > 3) {
            keep_going = 0;
        }
        i++;
    }
    printf("%d\n", i);
	return 0;
}

Part 2: 2D Loops (15 mins)

In this activity your tutor will run through the structure of a 2D while loop, hand-execute a loop and then will convert to a flowchart to working C code.

Tutor demo (8 mins)

The structure of a 2D while loop

structure of a while loop diagram

structure of a while loop diagram

Programming a 2D while loop

Convert the following flowchart to C code and hand execute the program.

example while loop diagram

Your Turn! (7 mins)

In groups of 3-4 match the following patterns to their code snippets:

A 
  OXXX
  XOXX
  XXOX
  XXXO
B 
  OXOX
  OXOX
  OXOX
  OXOX
C 
  OXOO
  XXXX
  OXOO
  OXOO
D 
  XXXX
  XOOX
  XOOX
  XXXX
1 
#include <stdio.h>

#define SIZE 4

int main(void) {
    int row = 0;
    while (row < SIZE) {
        int col = 0;
        while (col < SIZE) {
            if (col != 1 && row != 1) {
                printf("O");
            } else {
                printf("X");

            }
            col++;
        }
        row++;
        printf("\n");
    }
    return 0;
}
2 
#include <stdio.h>

#define SIZE 4

int main(void) {
    int row = 0;
    while (row < SIZE) {
        int col = 0;
        while (col < SIZE) {
            if (row == col) {
                printf("O");
            } else {
                printf("X");

            }
            col++;
        }
        row++;
        printf("\n");
    }
    return 0;
}
3 
#include <stdio.h>

#define SIZE 4

int main(void) {
    int row = 0;
    while (row < SIZE) {
        printf("X");
        int col = 1;
        while (col < SIZE - 1) {
            if (row == 0 || row == SIZE - 1) {
                printf("X");
            } else {
                printf("O");
            }
            col++;
        }
        printf("X");
        row++;
        printf("\n");
    }	
    return 0;
}
4 
#include <stdio.h>

#define SIZE 4

int main(void) {
    int row = 0;
    while (row < SIZE) {
        int col = 0;
        while (col < SIZE) {
            if (col % 2 == 0) {
                printf("O");
            } else {
                printf("X");

            }
            col++;
        }
        row++;
        printf("\n");
    }
	return 0;
}

Part 3: Scanning and Loops (15 mins)

In this section, we'll examine several problems that require scanning and loops. We'll then determine what type of loop involving scanning is required and write the loop condition for each program.

A: Enter a series of integers until you reach a negative number. Then, stop and calculate the sum. B: Enter characters until the user presses 'q'. Then, display the count of characters entered.
C: Scan for numbers until end of input and display all even numbers entered. D: Scan for integers keeping a cumulative sum, until the sum of entered integers reaches or exceeds the target sum provided by the user. Print the final sum.

Part 4: Structs and Enums (15 mins)

In this section we will create a program Coffee Shop which:

  1. Creates a struct coffee that stores the coffee type (an enum), the number of sugars and the size of a coffee
  2. Creates an enum coffee_type which defines the different types of drinks that can be ordered.
  3. The program will then take in a coffee order and store it in the struct.
  4. The program will then determine the price of the coffee based on the users order, outputting the price to the terminal (stdout).

The cost of the coffee will be determined by the following rules:

You will be working off of the starter code below:

// coffee_shop.c
//
// Written by YOUR-NAME (zID)
// on TODAYS-DATE 
//
// This program is a simple coffee shop used to demonstrate the use of 
// structs and enums in C. This program takes user input for a coffee order
// and outputs the cost of the order.

#include <stdio.h>

#define LARGE 'L'
#define REGULAR 'R'
#define ADDED_COST 0.5
#define BASE_COST 4.5

// TODO: Define an enum `coffee_type` that stores the different types of coffees 
// the shop sells. These are: LATTEE, CAPPUCCINO, ESPRESSO, AMERICANO & MATCHA.

// TODO: Define a struct `coffee` that stores 
// 1. the coffee type (an enum)
// 2. the number of sugars 
// 3. the size of a coffee 

int main(void) {
    // TODO: Initalise a variable for the struct

    printf("Enter coffee type (0: LATTE, 1: CAPPUCCINO, 2: ESPRESSO, \
            3: AMERICANO, 4: MATCHA): ");
    
    // TODO: take user input

    printf("Enter number of sugars: ");
    // TODO: take user input

    printf("Enter size (L for Large, R for Regular): ");
    // TODO: take user input

    // TODO: Calculate cost of order

	printf("Total cost: %.2lf\n", total_cost);
	return 0;
}