CODEWITHSUNDEEP
c
aquemini
aquemini

Reputation: 960

Character Comparison to Input in C

I'm a C amateur, and am tasked to write a program that takes command line arguments, one of which must be either the character 'N' or the character 'A'. This is the method that I thought would work effectively:

//check argv[2], valid should be 1 at this point if argv[1] is an integer
printf("Valid is currently: %d, valid);
printf("The second argument is: %s, argv[2]);
if(argv[2] != "N" && argv[2] != "A") { valid = 0; }
printf("Valid is currently: %d, valid");

Given the input ./a.out 4 A, and using printf statements before and after the given if statement, I achieve the following output:

Valid is currently: 1
The second argument is: A
Valid is currently: 0

I thought this would effectively make the valid-invalid bit invalid only if argv[2] wasn't "N" or "A", but it's not working. Then I tried to use strcmp in a similar code snippet, to unsuccessful results.

This is my first undertaking in C, so please be gentle, but I've tried everything from changing " to ', using strcmp instead of !=, and even using atoi, although I don't know if I used it properly. Is there something inherent in C string input or comparison I'm not understanding?

Upvotes: 1

Views: 83

Answers (1)

Jorge Israel Peña
Jorge Israel Peña

Reputation: 38586

To compare it as a string, try:

if (strcmp(argv[2], "N") != 0 && strcmp(argv[2], "A") != 0)
// can be reduced to:
if (strcmp(argv[2], "N") && strcmp(argv[2], "A"))

Or you can also compare it as a single character:

if (argv[2][0] != 'N' && argv[2][0] != 'A')

But that's probably not as versatile.

Upvotes: 3

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