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Today Xiaobian to share with you how to use the C language logic operators related knowledge points, detailed content, logic clear, I believe most people still know too much about this knowledge, so share this article for your reference, I hope you read this article after some gains, let's learn about it together.

I,&&& II Analysis

What are the values of i, j and k at the end of the following program?

#include int main(){ int i = 0; int j = 0; int k = 0; ++i || ++j && ++k; printf("i = %d\n", i); printf("j = %d\n", j); printf("k = %d\n", k); return 0;}

The output is as follows:

Why i = 1, j = 0, k = 0? See the analysis below.

Short circuit in program

|| Calculate from left to right:

Stop evaluating when a condition is true, the entire expression is true

An expression is false only if all conditions are false.

&& Calculate from left to right:

Stop evaluating when a condition is false, the entire expression is false

An expression is true only if all conditions are true

In logical expressions,&& is more than|| has a higher priority

In &&& and|| When mixed, the entire expression is treated as|| Expressions, the compiler starts evaluating && expressions from left to right, stops evaluating when one && expression is true, and the entire expression is true.

The above code can be explained. Since i = 0;++i is 1, true && ++i is 1, according to the short-circuit rule,|| It starts from left to right and stops when it meets a condition that is true, and the entire expression is true. So ++j and ++k are not running, so they are 0.

Here's another short-circuit rule in a program:

#include int g = 0; int f(){ printf("In f()...\ n"); return g++;} int main(){ if( g || f() && f() ) { printf("In if statement: %d\n", g); } printf("In main(): %d\n", g); return 0;}

Understand the short-circuit law and|| Mixing the algorithm with &&, the following output is easy to understand:

Two! analysis

Logical NOT in C! "I only know 0. I only know that when I see 0, I return to 1. So when it encounters a value other than 0, the result is 0. (Note that not only 1 means true, other non-zero values mean true)

Here's a snippet of code used by the logical NOT operator:

#include int main(){ printf("%d\n", ! 0); printf("%d\n", ! 1); printf("%d\n", ! 100); printf("%d\n", !- 1000); return 0;}

The output is as follows:

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