CSC 209 lab 10 solutions, week of 19 July 2022

Question 8:

Code:

int main(int argc, char **argv)
{
    if (argv[2] == NULL) {
        printf("two integers required on the command line");
        return(55);
    }
    printf("%d", atoi(argv[1]) + atoi(argv[2]));
}

Solution:

int main(int argc, char **argv)
{
    if (argc != 3) {
	fprintf(stderr, "usage: %s num1 num2\n", argv[0]);
        return(1);
    }
    printf("%d\n", atoi(argv[1]) + atoi(argv[2]));
    return(0);
}

Problems fixed above:

• The original check for argument count is bogus.
• That error message is actually a complaint about the usage, so it should be formulated as a standard usage error. Also, it was missing a newline.
• Errors go to stderr, not stdout.
• There's no reason for an error exit status of 55; avoid random numbers like this. If we have no particular reason to distinguish this error exit status, we use 1.
• Missing newline in successful printf().
• Missing return statement means that main() returns a somewhat random value in the success case. At the end of main() above we have a successful execution, so the return value, and hence the process exit status, should be zero.