Need a little help with programming in C#

   /* while loop will keep prompting user inputs EOF  */
            while (flag != EOF)
        {
                /*  user prompt will loop if while statement is true */
                printf("Enter annual interest rate (in decimal): ");
                flag = scanf("%f" ,&annual_interest);

                printf("Calculate compounding years, months or days?\n");
                printf("Enter '1' for years, '2' for months, '3' for days: ");
                flag = scanf("%f", &compound);

        if (compound = 1)
        {        printf("Enter number of years compounding: ");
                flag = scanf("%f" ,&years);
        }

        else if  (compound = 2)
        {       printf("Enter number of months compounding: ");
                flag = scanf("%f", &months);
                        years = months / 12;
        }

        else if (compound = 3)
        {       printf("Enter number of days compounding: ");
                flag = scanf("%f", &days);
                        years = days / 365;
        }