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Listing tasks

Learn to print tasks formatted with ListTasks.

The list_tasks function

To print all tasks we write the list_tasks function. A for loop runs from 0 to count and prints each task.

void list_tasks(struct Task tasks[], int count) {
    for (int i = 0; i < count; i++) {
        printf("%d %s %d\n", tasks[i].id, tasks[i].title, tasks[i].done);
    }
}

The function returns void; it only prints, it does not change anything. Exactly count tasks are printed.

Walking with a for loop

The pattern for (int i = 0; i < count; i++) starts at 0 and walks every element up to (but not including) count. i is the index, tasks[i] is the task at that index.

for (int i = 0; i < count; i++) {
    printf("%d %s\n", tasks[i].id, tasks[i].title);
}

This pattern is standard for walking arrays. The count bound marks the used part of the array.

Practice Add the list_tasks function

Add the void list_tasks(struct Task tasks[], int count) function to the code below. Inside it use a for (int i = 0; i < count; i++) loop to print each task as printf("%d %s %d\n", tasks[i].id, tasks[i].title, tasks[i].done);. In main replace the two printf calls with a list_tasks(tasks, count); call. Output should be 1 Shopping 0 and 2 Sport 0.

Starter code

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

struct Task {
    int id;
    char title[50];
    int done;
};

int add_task(struct Task tasks[], int count, const char *title) {
    tasks[count].id = count + 1;
    strcpy(tasks[count].title, title);
    tasks[count].done = 0;
    return count + 1;
}

int main(void) {
    struct Task tasks[10];
    int count = 0;
    count = add_task(tasks, count, "Shopping");
    count = add_task(tasks, count, "Sport");
    printf("%d %s %d\n", tasks[0].id, tasks[0].title, tasks[0].done);
    printf("%d %s %d\n", tasks[1].id, tasks[1].title, tasks[1].done);
    return 0;
}

Sample solution

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

struct Task {
    int id;
    char title[50];
    int done;
};

int add_task(struct Task tasks[], int count, const char *title) {
    tasks[count].id = count + 1;
    strcpy(tasks[count].title, title);
    tasks[count].done = 0;
    return count + 1;
}

void list_tasks(struct Task tasks[], int count) {
    for (int i = 0; i < count; i++) {
        printf("%d %s %d\n", tasks[i].id, tasks[i].title, tasks[i].done);
    }
}

int main(void) {
    struct Task tasks[10];
    int count = 0;
    count = add_task(tasks, count, "Shopping");
    count = add_task(tasks, count, "Sport");
    list_tasks(tasks, count);
    return 0;
}

Expected output

1 Shopping 0
2 Sport 0

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What is used to list all tasks?

  • A single printf
  • A for loop over all tasks Correct answer
  • An if statement
  • A switch

Explanation: A for loop walks all tasks from 0 to count.

2 Match listing concepts

Term Meaning
list_tasks listing function
for loop
count task count
%d %s %d print format

3 Loop bound

Question 
for (int i = 0; i < ____; i++) { /* print task */ }
Answer 
for (int i = 0; i < count; i++) { /* print task */ }

Explanation: Answer is count. i < count gives the right bound.

All lessons in Beginner

1 C basics

  1. What is C?
  2. Your first program
  3. Compile and run
  4. Comments
  5. printf and escapes
  6. Summary - C basics

2 Variables

  1. Declaring variables
  2. Variable assignment
  3. const
  4. Variable scope
  5. typedef
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. char
  4. sizeof
  5. Type conversion
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Menu loop
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Bitwise operators
  6. Summary - Operators

6 I/O

  1. printf formatting
  2. scanf
  3. Multiple inputs
  4. getchar and putchar
  5. puts and fputs
  6. Summary - I/O

7 Conditionals

  1. The if statement
  2. else and else if
  3. The switch statement
  4. The ternary operator
  5. Nested conditionals
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. break and continue
  5. Nested loops
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding products
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. Array size
  4. Multidimensional arrays
  5. Arrays and loops
  6. Summary - Arrays

11 Strings

  1. String basics
  2. String literals
  3. strlen
  4. strcpy and strcat
  5. strcmp
  6. Summary - Strings

12 Functions

  1. Defining functions
  2. Return values
  3. Parameters
  4. Function prototypes
  5. Recursion
  6. Summary - Functions

13 Pointer basics

  1. What is a pointer?
  2. The & address operator
  3. Pointer dereference
  4. NULL
  5. Pointer arithmetic
  6. Summary - Pointer basics

14 Arrays and pointers

  1. Array name as pointer
  2. Pointer to array
  3. Passing arrays to functions
  4. Pointer loop
  5. Multidim array pointer
  6. Summary - Arrays and pointers

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 String functions

  1. strchr
  2. strstr
  3. strtok
  4. sprintf
  5. sscanf
  6. Summary - String functions

17 Structs

  1. Defining structs
  2. Using structs
  3. typedef struct
  4. Array of structs
  5. Nested structs
  6. Summary - Structs

18 Memory and stack

  1. Stack and heap
  2. Automatic storage
  3. malloc
  4. free
  5. calloc and realloc
  6. Summary - Memory and stack

19 Preprocessor

  1. #define
  2. #include
  3. Conditional compilation
  4. Macro functions
  5. Header files
  6. Summary - Preprocessor

20 Beginner final

  1. Project design
  2. Data model
  3. Functions
  4. Memory management
  5. Putting it together