Thread: Problem with average

Hello, I have this problem,

Write a program for a professor to calculate the average grade of a student.The program should accept as many grades as the professor wants to enter.Therefore, ask the professor for the first grade, the second grade, and so onuntil the professor enters a negative value. A negative value indicates thatthe professor is finished entering grades. Once the professor is finished, yourprogram should output:a) the average grade of the studentb) the letter grade of the student

this is what I have so far.

Code:

#include <stdio.h>


int main ()
{
    double grade, s, total_firstgrade=0, total_secondgrade=0,average=0; //declare the variables


    do
    {
        printf("\nEnter the student grade: "); //asking the user to enter a integer
        scanf("%lf",&grade);
        printf
        if(f==-1||f<=0)
            break;
        else
        {
            printf("Enter the student grade: ");
            scanf("%lf",&s);


            //calculation of the average
            total_firstgrade+= f;
            total_secondgrade+= s;


            average:total_firstgrade+total_secondgrade/average;


        }
    } while (1);




        if (f<=0&& f!=-1)
            printf("first grade cannot be 0 or negative other than -1 to stop\n");


        if (total_firstgrade==0)
            printf("total first grade is 0, no average calculated\n");
        else
            printf("\nthe average of the student is: %lf\n",average);




    //using the if statement to find the student average grade
    if (s>100|| s,0)
        printf("non-valid average");
    else
    {
        if (s>=0)
            if (s<60)
            printf("F\n");
        else if (s<70)
            printf("D\n");
        else if (s<80)
            printf("C\n");
        else if (s<90)
            printf("B\n");
        else if (s<=100)
            printf("A\n");
    }
}

The thing is that it does not make the average. I would like to know what can I do to fix this problem. Thank You!