0.7 is not less than 0.7 but wrong result gets printed [duplicate]

问题

This question already has answers here:

strange output in comparison of float with float literal (8 answers)

Floating point comparison `a != 0.7` [duplicate] (3 answers)

Closed 5 years ago.

Here 'a' should get printed as 0.7 < 0.7 is false, but 'c' is printed.

#include<stdio.h>
void main()
{
  float a=0.7;
  if(a<0.7)
    printf("c");
  else
    printf("a");
}

回答1:

You seem to misunderstand floating point numbers. See this question.

One thing you can do is think "Well, it will never be exactly 0.7, so maybe I can't judge for sure, but I can get close...

Then, you pick a granularity, say, one millionth. You can try comparing the integer rounded result of ie6 * a to the integer rounded result of 1e6 * 0.7 to see not so much "is a < 0.7?", but "is a reasonably, close-enough, less than 0.7?"

Or, just compare to the same type. As said in the comments, maybe 0.7 is not a float literal but a double literal. Ensure it's a float literal to be sure, and 'a' is printed.

void main()
{
  float a=0.7;
  if(a<0.7f)
    printf("c");
  else
    printf("a");
}

来源：https://stackoverflow.com/questions/25458046/0-7-is-not-less-than-0-7-but-wrong-result-gets-printed