Homework Struggles

I am writing a program that will act as a simple calculator when it is complete. The instructions state to use one function that returns 2 output parameters and another to do the calculations. I am stuck trying to get my accumulator to keep the result. This version runs but the last input is always the output that is printed. Any hints?

Code:

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#include <stdio.h>
#include <math.h>


//Function prototypes
void scan_data (char *opp, double *nump);
void do_next_op (char op, double num, double *accup);

int main (void)

{
        //declare variables, not sure if the accumulator ACCU needs to be declared here
        double num, accu;
        char op;

        //Start do while loop to accept input from user until Q or q is chosen
        do
        {

        //Call functions until to get input and perform calculations
        scan_data(&op, &num);
        do_next_op (op, num, &accu);
        }
        while (op != 'q' && op != 'Q');

        //Print end result when Do While is exited
        printf ("The end result is %lf.\n", &accu);
}


//Get data function
void scan_data (char *opp, double *nump)

{
        double num;
        char op;
        printf ("Please enter an operator and number: ");
        scanf(" %c%lf", &op, &num);
        while (op != '+' && op != '-' && op != '*' && op != '/' && op != '^' && op != 'q' && op != 'Q')
                {
                fflush (stdin);
                printf ("Please enter an operator and Number: ");
                scanf(" %c %lf", &op, &num);
                }

                *opp = op;
                *nump = num;
}

//Here is where I think the problem lies, I reset the accumulator to 0 each time I enter the function, not sure how to fix it.
//I'm also not sure how to use the ACCU and *ACCUP as an input and output variable.
void do_next_op (char op, double num, double *accup)
{

        double accu = 0;

        if (op == '+')
        {
                *accup = accu + num;
                printf ("The result so far is %lf\n", *accup);
        }
        else if (op == '-')
        {
                *accup = accu - num;
        }

}

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Just some suggestions...

Try using more constants / defines for the different symbols and important input characters. Also, make your functions return 1 or 0 and check them with an if statement in your main to handle errors.

A compiler which warns you when you mess up printf/scanf is a good idea.

Code:

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$ gcc -Wall bar.c
bar.c: In function ‘main’:
bar.c:27: warning: format ‘%lf’ expects type ‘double’, but argument 2 has type ‘double *’
bar.c:28: warning: control reaches end of non-void function

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Also, see the FAQ on why fflush(stdin) is a bad idea.

In main you have to initialize accu = 0 when you define it.
In do_next_op() all you need to do is *accup = *accup + num. No need for variable 'accu'

Quote:

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Originally Posted by nonoob

In main you have to initialize accu = 0 when you define it.
In do_next_op() all you need to do is *accup = *accup + num. No need for variable 'accu'

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Thanks a lot, that did it. I was already playing with *accup = *accup + num, the initialization fixed it.

1) Return 0 at the end of main

2) Test often and compile after every single instruction.