true/false question

[Bachstelze]

Standard C doesn't have a boolean variable.

I am not sure what you mean by "a boolean variable", but standard C certainly does have a bool type since C99. Also note sure what "this" refers to in

...this works with any data type, not just int, AFAIK.

EDIT: Okay...

You can, but for your purposes, you probably don't need to.

Just set it to 1 (or more) or 0, depending on how you take input.

What is this? There is a type bool, its purpose is to represent boolean values. Of course you don't "need" to use it, and you don't "need" to use an int, either. You could use a float, or a struct, or whatever. But a bool is the right thing to use. Not an int or anything else.

[Bachstelze]

What I said above notwithstanding, just because a variable can only take two values does not necessarily mean it should be made a bool. A bool can not take any two values, it can only take the values true and false. This is a good use of bool:

bool found = false;
for (int i=0; i<n; i++) {
    if (t[i] == SOME_VALUE) {
        found = true;
    }
}

This is a bad one:

bool turn = true;
for (;;) {
    /* Play */
    turn = !turn;
}

it should be:

#define WHITE 1
#define BLACK 0

int turn = WHITE;
for (;;) {
    /* Play */
    turn = (turn == WHITE) ? BLACK : WHITE;
}

A good rule of thumb is: add a question mark after the name of your variable. If you can answer the resulting question with yes or no, make it a bool. Otherwise, don't.

[littlerunaway]

So i do need to use a bool type variable?that's my problem. Do i give an initial value of true or 1? and how do i check which value it holds? with frog=1 condition?

[littlerunaway]

I meant frog ==1 of course

[dwhitney67]

var = !var will work, try it.

Yep.

Another way (assuming var is initialized to either 0 or 1)...

var ^= 1;

And with C99 style:

#include <stdbool.h>
...
bool var = false;
...
var ^= true;

[littlerunaway]

We haven't learnt that one so im not sure what it means

[dwhitney67]

I meant frog ==1 of course

You can do that. A simple if/else is all that is required. Depending on circumstances, it is sometimes helpful to use a terciary-style of statement.

Examples:

#include <stdbool.h

int main(int argc, char** argv)
{
    bool args_given = (argc > 1);

    if (args_given)
    {
        // parse command-line options
    }
    else
    {
        // no command-line options given
    }
    ...
    return 0;
}

...
printf("The value is %s\n", (value ? "true" : "false"));
...

[Bachstelze]

So i do need to use a bool type variable?that's my problem. Do i give an initial value of true or 1? and how do i check which value it holds? with frog=1 condition?

What does "frog" even mean? Whether you should make it a bool or not depends on this. In any case, as such it most likely fails the bool test of my post #12.

[littlerunaway]

Frog is a variable that should get true or false. how the programs behaves depends on what frog hold. frog also should change between 1&0 under the same conditions

[Bachstelze]

That's not what I meant. Why is your variable named "frog"?