can anyone please explain why this code is outputting "true"?

Question

1.00/5 (1 vote)

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C++

#include<stdio.h>
int main(){
float a=0.7;
if(a<0.7){
printf("true");
}
else{
printf("false");
}
return 0;
}

Posted 26-Nov-15 18:32pm

Member 12169899

Updated 26-Nov-15 18:43pm

PIEBALDconsult

v3

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PIEBALDconsult 27-Nov-15 0:44am

Try printing the value of a and/or use the debugger to see it.

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PANKAJMAURYA · Answer 1 · 2015-11-26T19:02:00

Any thing you write in code must be stored in memory in binary form (0,1 form)
When you write float a=0.7 then a must get the binary value of 0.7.
In binary 0.7 is

C#

b0.1011001100110011001100110011001100110011001100110011001100110...

However, 0.7 is a double-precision literal, whose value is 0.7 rounded to the closest representable double-precision value, which is:

C#

b0.10110011001100110011001100110011001100110011001100110

In decimal, that's exactly:

C#

0.6999999999999999555910790149937383830547332763671875

When you write float a = 0.7, that double value is rounded again to single-precision, and a gets the binary value:

C#

b0.101100110011001100110011

which is exactly

C#

0.699999988079071044921875

in decimal.
When you do the comparison (a < 0.7), you are comparing this single-precision value (converted to double, which does not round, because all single-precision values are representable in double precision) to the original double-precision value.

C#

0.699999988079071044921875 < 0.6999999999999999555910790149937383830547332763671875

the comparison correctly returns true.
Please visit this link for Floating point airthmatic operation
Floating Point Airthmatic[^]

Animesh Datta · Answer 2 · 2015-11-26T19:07:00

Hello ,
In C programming language, the floating point constant is double type by default, that's why 0.7 is double type, unless use 'f' or 'F' suffix to indicate float type.Hence the float variable a is less than double constant 0.7.

#include<stdio.h>
int main()
{
    float a=0.7;
    printf("%.10f %.10f\n",0.7, a);
    return 0;
}
</stdio.h>

O/P will be

0.7000000000 0.6999999881

Hence the if condition is satisfied and it prints "true"

can anyone please explain why this code is outputting "true"?

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