Calculate average of each line of input

Question

I made a program that will loop and calculate the average of the input given by the user. There are no problems here. I just want to know if there is a better way to do this, or a way to optimize this code.

How this program works:

First, the program will read a double and a separator in a forever loop until it finds a newline character or a wrong separator. If it finds a space as separator, then it will just continue to read more input. If it finds newline, then it will print the average. If it finds anything else separator, e.g. 'a' or '^', then it will print "error!".

The code:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
    double average, num, total;
    char separator;

    for(int i = 1; ; i++) //increment the value as the loop goes
    {
        scanf("%lf%c", &num, &separator);
        total += num;

        if(separator == '\n')
        {
            average = total / i;
            printf("average = %lf\n", average);
            break;
        }
        else if(separator == ' ')
        {
            //do nothing
        }
        else
        {
            while((getchar()) != '\n'); //clear buffer
            printf("error!\n");
            break;
        }
    }

    printf("press ENTER to exit...");
    getchar();
    return 0;
}

Answer 1

Since we don't use any arguments, we could use int main(void) instead.

If we don't successfully read a number, scanf will return 0. But we ignore that and use num anyway, indefinitely (since the input position is never advanced).

The scope of all the variables can be reduced to within the for loop.

while((getchar()) != '\n'); will continue looping indefinitely if the input stream is closed (since EOF != '\n'). Consider ignoring the rest of line with a single call to scanf("%*[^\n]") instead. Alternatively, return EXIT_FAILURE to indicate the problem.

Error messages should go to stderr rather than stdout.

The final printf() and getchar() make it harder to use your program as a filter in a pipe. I would just drop them (and the return 0; that's implied by reaching the end of main()).

Answer 2

the variable total is never initialized, then it is used as a source value in total += num; which results in undefined behavior.

the posted code does not re-initialize after the '\n' is processed znc your problem description fails to clarify what the proper action should be.