Week 2 Code Examples

// A program to revise the following concepts
// Declaring, initialising, modifying and printing variables of types
// int, double, char
// Using simple mathematical operators
//
// Written by: Angela Finlayson
// Date: 16/09/2026
//
// This program prints out details of the player's initials
// gold and health
// The gold and health get updated.


#include <stdio.h>

int main(void) {
    int gold = 10;
    double health = 85;
    char initial = 'X';

    printf("Player: %c\n", initial);
    printf("Gold: %d Health: %.2lf\n", gold, health);

    gold = gold + 1; //10 + 1 = 11
    health = health / 2; //85 / 2 = 42.5 
    printf("Gold: %d Health: %.1lf\n", gold, health);

    // How could we print to 1 decimal place?
    return 0;
}

// A program to revise the following concepts
// Using scanf to read in data from the user of types
// int and double
//
// Written by: Angela Finlayson
// Date: 16/09/2026
//
// This program reads in integer coordinates and a real value for a length

#include <stdio.h>

// In class
// Show error input - see how to handle this later today!!

int main(void) {
    int x;
    int y;
    printf("Enter coordinates: ");
    scanf("%d %d", &x, &y);
    printf("You entered (%d, %d)\n", x, y);
    
    double length;
    printf("Enter length: ");
    scanf("%lf", &length);
    printf("You entered %lf\n", length);

    return 0;
}

// This is an example of using constants 
// to give meaning to values used in our code 

#include <stdio.h>

#define STARTING_GOLD 100
#define SWORD_COST 40
#define SHIELD_COST 30
#define POT_OF_GOLD 50


int main (void) {
    int gold = STARTING_GOLD;
    gold = gold - SWORD_COST;
    gold = gold + POT_OF_GOLD;
    gold = gold - SHIELD_COST;
    printf("Gold: %d\n", gold);

    return 0;
}

// This is an example of use magic numbers
// A magic number is an unnamed hardcoded value whose meaning is unclear.
// Compare this code to the code in constants.c that 
// replaces magic numbers with #define constants

#include <stdio.h>

int main (void) {
    int gold = 100;
    gold = gold - 40;
    gold = gold + 50;
    gold = gold - 30;
    printf("Gold: %d\n", gold);

    return 0;
}

// Write a program to allow a user to enter a character
// Print out whether the character is an uppercase letter,
// a lowercase letter, or not a letter.

#include <stdio.h>

int main(void){
    // Do we want to use " %c" or "%c"
    char input;
    printf("Enter a character: ");
    scanf("%c", &input);

    if (input >= 'a' && input <= 'z') {
        printf("Lowercase\n");
    } else if (input >= 'A' && input <= 'Z') {
        printf("Uppercase\n");
    } else {
        printf("Not a letter\n");
    }

    

    return 0;
}

// Demonstration of nested if statements
// Written by: Angela Finlayson
// Date: 20/09/2026

// $ ./game_level
// Did you complete the level? (y/n): n 
// Keep playing!

// $ ./game_level
// Did you complete the level? (y/n): y 
// How many coins did you collect? 10 
// Bonus: 3 stars! 

// $ ./game_level
// Did you complete the level? (y/n): y 
// How many coins did you collect? 9 
// Bonus: 1 star! 


#include <stdio.h>
#define MAX_COINS 10

int main(void) {    
    char input;
    printf("Did you complete the level? (y/n) ");
    scanf(" %c", &input);

    if (input == 'y') {
        printf("How many coins did you collect? ");
        int gold;
        scanf("%d", &gold);
        if (gold >= MAX_COINS) {
            printf("Bonus: 3 stars!\n");
        } else {
            printf("Bonus: 1 star!\n");
        }

    } else if (input == 'n'){
        printf("Keep Playing!\n");
    }
    
    return 0;
}

// Write a program guessing_game.c that 
// prompts the user enter an integer
// prints out higher, lower, correct if it is equal to the secret number (42)

// $ ./guessing_game 
// Please enter an integer: 8
// Higher!
// $ ./guessing_game 
// Please enter an integer: 42
// Correct!

#include <stdio.h>
#define SECRET_NUMBER 42

int main(void){
    int guess;
    printf("Please enter an integer: ");
    int num_read = scanf("%d", &guess);

    if (num_read != 1){
        printf("Incorrect Usage: enter an integer\n");
    } else if (guess == SECRET_NUMBER) {
        printf("Correct!\n");
    } else if (guess > SECRET_NUMBER) {
        printf("Lower!\n");
    } else {
        printf("Higher\n");
    }

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

// Demonstration of simple if statements
// with simple conditions
// 
// Written by: Angela Finlayson
// Date: 18/09/2026

#include <stdio.h>

int main(void) {    
    // Note the indentation
    if (1) {
        printf("Hooray\n");
    }

    if (0) {
        printf("Yay!\n");
    }
          
    if (4 == 4) { 
        printf("I love C!\n");
    }
    
    if ('Z' == 'z') {
        printf("I am cool!\n");
    }

    int x = 5;
    int y = 10;

    if (x < 0) {
        printf("x is negative!\n");
    }

    if (y >= x) {
        printf("y is greater or equal\n");
    }

    if (x != y) {
        printf("x and y not equal!\n");
    }

    printf("I love if statements!\n");
    return 0;
}

// Demonstration of nested if statements
// 
// Written by: Angela Finlayson
// Date: 18/09/2026

#include <stdio.h>

int main(void) {    
    int x;
    
    printf("Enter an integer: ");
    scanf("%d", &x);

    if (x > 0) {
        if (x > 100) {
            printf("big");
        } else {
            printf("small");
        }
        printf(" positive");
    } else {
        printf("Not a positive");
    }

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

// Write a program odd_even.c that 
// prompts the user enter an integer
// prints out whether the number is even or odd
//
// $ ./odd_even 
// Please enter an integer: 8
// Even!
// ./odd_even 
// Please enter an integer: 3
// Odd!

#include <stdio.h>

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

    if (value % 2 == 0) {
        printf("Even\n");
    } else {
        printf("Odd\n");
    }
    

    return 0;
}

// Demonstration of error checking using the return value from scanf
// 
// Written by: Angela Finlayson
// Date: 18/09/2026

#include <stdio.h>

int main(void){  
    int x; 
    int y;
    double z;

    printf("Enter 2 integers and real number: ");
    int inputs_read = scanf("%d %d %lf", &x, &y, &z);
    printf("%d inputs were read in\n", inputs_read);
    
    if (inputs_read == 3) {
        printf("Inputs were: %d %d %lf\n", x, y, z);
    } else {
        printf("Incorrect usage: Enter 2 integers and real number\n");
    }
    return 0;
}

// Demonstration of chained else if statements
// with simple conditions
// 
// Written by: Angela Finlayson
// Date: 18/09/2026

#include <stdio.h>
#define COLD 10
#define HOT 25

// What test cases should we use?
int main(void) {    
    int temperature;
    printf("Please enter the temperature: ");
    scanf("%d", &temperature);
    
    if (temperature <= COLD) {
        printf("I am cold!\n");
    } else if (temperature < HOT) {
        printf("Just right!\n");
    } else {
        printf("I am hot!\n");
    }
    
    printf("Have a nice day\n");
    return 0;
}

// Demonstration of conditional while loops
// We do not know exactly how many times the loop will repeat
// There is no specific input value that stops it
// There is just a condition
// Written by: Angela Finlayson
// Date: 19/09/2026

#include <stdio.h>
#define MAX_KOMBUCHA 2000

int main(void) {
    // 1. Initialise the loop control variable
    int total_kombucha_ml = 0;
    int kombucha_ml;
    while (total_kombucha_ml < 2000) { // 2. Test the loop condition
        printf("Please enter the ml of kombucha: ");
        scanf("%d", &kombucha_ml);
        // 3. Update loop control variable
        total_kombucha_ml = total_kombucha_ml + kombucha_ml; 
    }												
    printf("Kombucha target reached %d!!\n", total_kombucha_ml);
    return 0;
}

// Demonstration of conditional while loops
// We do not know exactly how many times the loop will repeat
// There is no specific input value that stops it
// There is just a condition
// In this example we use a flag variable to control the loop
// Written by: Angela Finlayson
// Date: 19/09/2026

#include <stdio.h>

int main(void) {  
    int pin;
    int confirmation;
    int pins_match = 0;


    while (pins_match == 0) {
        printf("Enter a PIN: ");
        scanf("%d", &pin);
        printf("Enter the PIN again: ");
        scanf("%d", &confirmation);
        if (pin == confirmation) {
            pins_match = 1;
        } 
    }
    printf("PIN saved!\n");
    return 0;
}

// Demonstration of counting while loops
//
// Written by: Angela Finlayson
// Date: 18/09/2026

#include <stdio.h>
#define MAX 3

//Trace with 3
//Try going backwards
int main(void) {    
    // 1. Initialise loop counter before the loop
    int counter = 0;
    while (counter < MAX) { // 2. check loop counter condition
        printf("%d Here we go loop de loop!\n", counter);
        counter = counter + 1; // 3. update loop counter
    }

    // What will this print?
    printf("%d Yay the loop ended!!!\n", counter);
    return 0;
}

// Demonstration of infinite while loops
// Typically you do not want an infinite loop!
// Type Ctrl+C to end program.
//
// Written by: Angela Finlayson
// Date: 18/09/2026

#include <stdio.h>

int main(void) {   
    // Change to a while loop 
    while (1) {
        printf("I love my COMP1511/1911 lectures!\n");
    }


    // Infinite loop
    // How could we stop it?
    // int push_ups = 0;
    // while (push_ups < 10) {
    //      printf("You have done %d push-ups!\n", push_ups);
    // }
    // printf("Congratulations you have done %d push-ups!\n", push_ups);

    return 0;
}

// Modify this code to calculate the sum of all integers entered
// by the user
// The loop should end when the user enters non-integer data
//
// Written by: Angela Finlayson
// Date: 20/09/2026

#include <stdio.h>

int main(void) {  
    
    return 0;
}

// Demonstration of sentinel while loops
// A sentinel value as a specific input value that terminates the loop
// Written by: Angela Finlayson
// Date: 18/09/2026

#include <stdio.h>

int main(void) {    
    char grade;
    printf("Enter a grade (q to quit): ");
    
    scanf(" %c", &grade);
    // Stop when we reach the sentinel value 'q'
    while (grade != 'q') {
        printf("You entered %c\n", grade);
        printf("Enter a grade (q to quit): ");
        scanf(" %c", &grade);
    }
    return 0;
}