为什么条件语句中的负数为真? [英] why negative number is taken as true in condition statement?

问题描述

在这里，我对带有负数的条件语句感到困惑，如果在条件中仅给出负数，如(-1)则为true，但如果(-1> 0)则为false，请解释任何一个预先感谢

Here i am confused with condition statement which has negative number,if in the condition only negative number is given as if(-1) then it is true but if (-1>0) then it become false please explain any one thanks in advance

if(-1) // This true why and how?
if(-1>0)//This is false why and how

现在下面的代码有什么影响，请帮助理解

Now what is impact in below code please help to understand

#include <stdio.h>
#include <string.h>

main()
{
  char a[]="he";
  char b[]="she";
  if(strlen(a)-strlen(b)>0)//how it is true ?if(2-3>0)i.e if(-3>0) which is false
    //here why it is true                   
  {
    printf("-ve greater then 0 ");
  }
  else 
  {
    printf(" not greater then 0");
  }
}

推荐答案

if(-1)//这是正确的原因和方式?

if(-1) // This true why and how?

任何非零数字都将被评估为 true .

Any non-zero number is evaluated as true.

if(-1> 0)//这是错误的原因和方式

if(-1>0) //This is false why and how

-1 小于 0 ，这就是表达式 -1>0 评估为 false .

-1 is less than 0 that's why expression -1 > 0 evaluated to false.

if(strlen(a)-strlen(b)> 0)//它是如何正确的?if(2-3> 0)ie if(-3> 0)错误的//这里为何如此

if(strlen(a)-strlen(b)>0) //how it is true ?if(2-3>0)i.e if(-3>0) which is false //here why it is true

strlen 返回 size_t 类型，该类型为 unsigned . strlen(a)-strlen(b 的结果将是 unsigned int .但是 -1 的结果不是 unsigned >，因此在比较之前将其转换为 unsigned . strlen(a)-strlen(b)> 0 将导致比较 UINT_MAX -1> 0

strlen returns size_t type which is unsigned. The result of strlen(a)-strlen(b would be an unsigned int. But -1 in not unsigned, therefore it is converted to unsigned before comparison.strlen(a)-strlen(b)>0 will result in comparison UINT_MAX -1 > 0

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