'If' Condition Not Working As Expected In My C Code

Question

I am fully aware that this is due to some error overlooked by me while writing my text-based calculator project in C, but I have only started learning C less than a week ago, so please help me out!

Since the entire code is 119 lines, I'll just post the necessary snippet where the real issue lies: (There are no errors during compiling, so there is no error beyond these lines)

char choice[15];
    printf("Type 'CALCULATE' or 'FACTORISE' or 'AVERAGE' to choose function :\n");
    gets(choice);
    if (choice == "CALCULATE")

The bug is that even after perfectly entering CALCULATE or FACTORISE or AVERAGE, I still get the error message that I programmed in case of invalid input (i.e, if none of these 3 inputs are entered). It SHOULD be going on to ask me the first number I wish to operate on, as written for the CALCULATE input.

The code runs fine, no errors in VS 2013, and so I'm sure its not a syntax error but rather something stupid I've done in these few lines.

You don;t use `==` to compare string in C. You use `strcmp()` — Sourav Ghosh, Jun 15 '20 at 05:20
Right, thanks, I'm coming from Python.... So what exactly should i do ? — An Ant, Jun 15 '20 at 05:21
Does this answer your question? [How do I properly compare strings?](https://stackoverflow.com/questions/8004237/how-do-i-properly-compare-strings) — kaylum, Jun 15 '20 at 05:21

score 0 · Accepted Answer · answered Jun 15 '20 at 05:21

0

If you use == you are comparing the addresses of 2 arrays, not the contents of the arrays.

Instead, you need to do:

if (strcmp(choice, "CALCULATE") == 0)

answered Jun 15 '20 at 05:21

cigien

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Thanks, that should fix it. I havent studied arrays yet, I was just going by what I had learnt from Python. – An Ant Jun 15 '20 at 05:25
I'm not sure what you're question is, but that should be a separate question. – cigien Jun 15 '20 at 06:29

score 0 · Answer 2 · answered Jun 15 '20 at 05:22

0

Two things to mention here:

Never use gets() it has serious security issues and is removed from the latest standard. Use fgets() instead.
To compare strings, you should use strcmp(), not ==.

answered Jun 15 '20 at 05:22

Sourav Ghosh

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fgets() avoids buffer overflow, true, but increases unnecessary steps, and to be real, it is mostly only me who will use this project. – An Ant Jun 15 '20 at 05:26
@AnAnt Whatever be the case, if you want to write correct and standard complaint code, you **cannot** use `gets()`. – Sourav Ghosh Jun 15 '20 at 05:27
I'm coding for myself, and i respect you standardised instincts, but for me and 4 of my friends it really wouldnt matter that much right ? – An Ant Jun 15 '20 at 05:32
@AnAnt take your pick, but I'd suggest, if you're doing something, do it right. – Sourav Ghosh Jun 15 '20 at 05:34

score 0 · Answer 3 · answered Jun 15 '20 at 05:24

0

The problem is you're trying to compare a string literal with a char array. C isn't found those things being the same, since the '==' comparison operator is not implemented in that way.

You have two options for performing that comparison :

1) Use the strcmp() function, from string.h library

2) Manually comparing the chars in your array, and the string literal

Definitely, the first option is the easiest and cleanest one.

answered Jun 15 '20 at 05:24

Oscar Cuadrado

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thanks, that I'll do this. I'm coming from Python, so I did it almost reflexively. – An Ant Jun 15 '20 at 05:27

'If' Condition Not Working As Expected In My C Code

3 Answers3