what is the meaning of == sign?

I am trying to figure out what =开发者_Python百科= sign means in this program?

int main()
{
    int x = 2, y = 6, z = 6;        
    x = y == z;
    printf("%d", x);
}

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The == operator tests for equality. For example:

if ( a == b )
    dosomething();

And, in your example:

x = y == z;

x is true (1) if y is equal to z. If y is not equal to z, x is false (0).

A common mistake made by novice C programmers (and a typo made by some very experienced ones as well) is:

if ( a = b )
    dosomething();

In this case, b is assigned to a then evaluated as a boolean expression. Sometimes a programmer will do this deliberately but it's bad form. Another programmer reading the code won't know if it was done intentionally (rarely) or inadvertently (much more likely). A better construct would be:

if ( (a = b) == 0 )   // or !=
    dosomething();

Here, b is assigned to a, then the result is compared with 0. The intent is clear. (Interestingly, I've worked with C# programmers who have never written pure C and couldn't tell you what this does.)

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It is "equals" operator.

In the above example, x is assigned the result of equality test (y == z) expression. So, if y is equal to z, x will be set to 1 (true), otherwise 0 (false). Because C (pre-C99) does not have a boolean type, the expression evaluates to an integer.

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Equality. It returns 1 if the operands are equal, 0 otherwise.

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== means "is euual to". This operator has higher precedece than = (equal to) operator. So the equation x = y == z; will try to assign result of y==z to variable x. which is 1 in this case.

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int main() 
{ 
    int x = 2, y = 6, z = 6;         
    x = y == z; 
    printf("%d", x); 
} 

let`s start like this:

 x = (6==6)

It asks is 6 equivalent to 6?: true

x = true, but since x is an int, x= 1 The new value of x is 1.

The following is printed:

1

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It's saying

X will equal either true/1 or false/0.

another way to look at that line is this:

x =  ( is y equal to true? then true/1 or false/0 )

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== operator used for equality.. here in u r example if y is equal to z then x will hav true value otherwise x will hav false

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Think about it like this:

= means give something a value.

== means check if it is equal to a value.

For example

int val = 5; //val is 5
//= actually changes val to 3
val = 3; 

//== Tests if val is 3 or not. 
//note: it DOES NOT CHANGE the value of val.
val == 3; 

int new_val = val == 3; //new_val will be 1, because the test is true

//the above statement is the same as
bool is_val_3 = false;
if( val == 3 )
   is_val_3 = true;
int new_val;
new_val = is_val_3;

//putting it together, 
val = new_val == 2; //sets val to 0. do you understand why now?