undefined reference to～によるエラーの解決法

C言語で、タスク情報を記録できるシステムを作成しています。以下のソースコードから実行しようとすると
C:\Users\AppData\Local\Temp\ccQhtmBp.o:qq.c:(.text+0x3c): undefined reference to edittask' C:\Users\\AppData\Local\Temp\ccQhtmBp.o:qq.c:(.text+0x43): undefined reference to deletetask'
のエラーが表示されプログラムがうまく実行できません。
エラーの原因及び修正箇所の提示をご教授していただけると幸いです。

c
#include <stdio.h>

void addtask();
void viewtask();
void edittask();
void deletetask();
char menu();

int main() {
    char selection ;
   do {
    selection = menu();
    switch(selection) {
        case '1': addtask(); break;
        case '2': viewtask(); break;
        case '3': edittask(); break;
        case '4': deletetask(); break;
        case '5': break;
        default: printf("Invalid option");
    }
   }while(selection != '1');
   return 0;
}

char menu() {
    char option;
    printf("\n1) Add New Task");
    printf("\n2) View Task");  
    printf("\n3) Edit Task");
    printf("\n4) Delete Task");
    printf("\n5) Exit");
    printf("\nEnter option: ");
    scanf("%c[^\n]", &option);
    return option;
}

void addtask( ){
    int utask, duedate, status, category, note;
    printf("\n\n\t\t---------------------------------\n");
    printf("\t\t* Welcome to Add Task Menu! *");
    printf("\n\t\t---------------------------------\n\n");

    FILE * f = fopen("task.txt", "r+");
    if(f == NULL)
            f = fopen("task.txt", "w");
    else {
            fseek(f, 0, SEEK_END); 
            printf("\nEnter your Task name:");
            scanf("%s", &utask); 
            printf("\nEnter your Task due date[yyyy-mm-dd]: ");
            scanf("%d", &duedate); 
            printf("\nENTER progress percentage[0.00~100]:");
            scanf("%f", &status); 
            printf("\nEnter category: ");
            scanf("%s", &category); 
            printf("\nEnter Note: ");
            scanf("%s", &note); 
            fprintf(f,"%s %d %f %s %s\n", utask, duedate, status, category, note); 
    }
    fclose(f);
}

void viewtask(){
  int na, d, s, c, no;
  printf("\nThis is Your task details");
  FILE * f = fopen("task.txt", "r");
  while(fscanf(f,"%s",&na) != EOF){ 
        fscanf(f,"%d",&d);
        fscanf(f,"%f",&s);
        fscanf(f,"%s",&c);
        fscanf(f,"%s",&no);
        printf("\nYour Task: %s \t Task duedate: %d \t Task progression: %f \t Task category: %s \t Task note: %s",na, d, s, c, no);
    }
    fclose(f);
}

void update() {
    int utask, d, s, c, no, na;
    FILE * f = fopen("task.txt", "r");
    FILE * ft = fopen("tmp.txt", "w");
    printf("\nthis is edit task"); //変更
    printf("\nEnter your task:");
    scanf("%s", &utask); 
    while(fscanf(f,"%s",&na) != EOF){  
        fscanf(f,"%d",&d);
        fscanf(f,"%f",&s);
        fscanf(f,"%s",&c);
        fscanf(f,"%s",&no);
        if(na == utask){
            printf("\nUpdating >> your task: %s \t duedate: %d \t stasus: %f \t category: %s \t note: %s", na, d, s, c, no);
            printf("\nEnter new duedate:");
            scanf("%d", &d);
            printf("\nEnter new progression:");
            scanf("%f", &s);
            printf("\nEnter new category:");
            scanf("%s", &c);
            printf("\nEnter new note:");
            scanf("%s", &no);
        }
        fprintf(ft,"%s %d %f %s %s\n", na, d, s, c, no);  
    }
    fclose(ft);
    fclose(f);  
    remove("task.txt");
    rename("tmp.txt", "task.txt");
}

void delete() {
    int utask, d, s, c, no, na;
    FILE * f = fopen("data.txt", "r");
    FILE * ft = fopen("tmp.txt", "w");
    printf("\nthis is delete record");
    printf("\nEnter utask:");
    scanf("%d", &utask); 
    while(fscanf(f,"%s",&na) != EOF){
        fscanf(f,"%d",&d);
        fscanf(f,"%f",&s);
        fscanf(f,"%s",&c);
        fscanf(f,"%s",&no);
        if(na == utask){
            printf("\nDelete -> your task: %s \t duedate: %d \t progression: %f \t category: %s \t note: %s", na, d, s, c, no);
            continue;
        }
        fprintf(ft,"%s %d %f %s %s\n", na, d, s, c, no);  
    }
    fclose(ft);
    fclose(f);    
    remove("task.txt"); 
    rename("tmp.txt", "task.txt"); 
}