hey ,
i'm having a problem with a LINK error i keep getting the same error although deleted the line with the flushall_
also i copyed the code in a new project but it still gives me the same error

the error :

  Error 1   error LNK2019: unresolved external symbol _flushall_ referenced in function _main   C:\Users\Naya123\Desktop\proj1\proj1\q1.obj proj1





 #include<stdio.h>
#include<math.h>
#include<string.h>
void main()
{
    char option; int num1, num2, num3,count=0,num,base;
    menue();
    scanf_s("%c",&option);
    while (option != 'Y' || option != 'y')
    {
        switch (option)
        {
        case 'a' :
        case 'A':
            printf("insert first number : "); scanf_s("%d", &num1);
            printf("insert seconde number : "); scanf_s("%d", &num2);
            printf("insert third number : "); scanf_s("%d", &num3);
            printf("the max between these three is %d \n ", max(num1, num2, num3));
            break;
        case 'B' :
        case 'b':
            printf("insert first number : "); scanf_s("%d", &num1);
            printf("insert seconde number : "); scanf_s("%d", &num2);
            printf("insert third number : "); scanf_s("%d", &num3);
            printf("the min \n");
            //printf("the min  between these three is %d \n ", min(num1, num2, num3));
            break;
        case 'C':
        case 'c':
            printf("insert  number : "); scanf_s("%d", &num);
            if (is_positive(num) == ERROR)
            {
                printf("Error back to menue \n");
                break;
            }
            else {
                printf("the oposite of the number is %d \n ", oposite(num));
                break;
            }
        case 'D':
        case 'd':
            printf("insert  number : "); scanf_s("%d", &num);
            if (is_positive(num) == ERROR)
            {
                printf("Error back to menue \n");
                break;
            }
            else {
                printf("the oposite of the number is %d \n ", (is_polendrom(num)== 0) ? "the number isn't a polindrom \n" : "the number is a polindrom \n");
                break;
            }
        case 'E':
        case 'e':
            printf("insert  number : "); scanf_s("%d", &num);
            if (is_positive(num) == ERROR)
            {
                printf("Error back to menue \n");
                break;
            }
            else {
                printf("insert  the base: "); scanf_s("%d", &base);
                printf("the number in a detcimal base is  %d \n ", numByBase10(num,base));
                break;
            }
        case 'F':
        case 'f':
            printf("insert  number : "); scanf_s("%d", &num);
            if (num < 0)
                num = (make_bolindrom(-1 * num))*-1;
            else num = make_bolindrom(num);
            break;
        case 'G':
        case 'g' :
            printf("DoYou Really want to quit? y/n \n");
            option=getchar(); enter=flushall_();
            if (option == 'Y' || option == 'y')
                printf("thx for using the system ! byee \n");
            else 
                menue();

            break;


        }
        if (option != 'Y' || option != 'y')
        {
            menue();
            scanf_s("%c",&option);
        }
    }
}