How can we write "not equal" in c?

Question

In part of a code I saw this phrase:

!(word[i]==(tmpP->word[i]))

is it equal to

(word[i] != (tmpP->word[i]))

?

What is the difference between these two expressions?

Answer 1

The expression

!(word[i]==(tmpP->word[i]))

is logically equivalent to the expression

(word[i] != (tmpP->word[i]))

Another example

!( a == b && c == d )

is equivalent to

!( a == b ) || !( c == d )

that is, in turn, equivalent to

a != b || c != d

Answer 2

what is the difference between these two expressions?

One can use a != b or !(a == b) interchangeably¹. Both use a, b once and both evaluate to an int of value 0 or 1.

Use the one most clear for the context of code (which is usually the first, but the seconds binds tighter.)

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How can we write "not equal" in c?

Standard C has alternate spellings macros in <iso646.h> (since C94) including not_eq.

and     &&
and_eq  &=
bitand  &
bitor   |
compl   ~
not     !
not_eq  !=
or      ||
or_eq   |=
xor     ^
xor_eq  ^=

Example

#include <iso646.h>
#include <stdio.h>
#include <time.h>

int main() {
  srand((unsigned)time(0));
  int a = rand()%2;
  int b = rand()%2;
  if (a not_eq b) puts("Not equal.\n");
  else puts("Equal.\n");
}

Use <iso646.h> with caution as the macros may collide with existing code names.

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¹ ! has higher precedence than !=, so with more complex expressions, be careful. When in doubt, use an outer (): (a != b) versus (!(a == b)) are truly the same.