beginner question double data type

I am beginner in c programming, As far as I understand it is used to store decimal number and float number.

Code:

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#include <stdio.h> int main()
{
    int a = 1;
    char b ='G';
    double c = 3.14;
    printf("a = %d\n", a);
    printf("b = %c\n", b);
    printf("c = %lf\n", c);
 
    return 0;
}

---

a = 1
b = G
c = 3.140000


but there is already int type to store decimal and float to store float number so what's the specific use of double data type in C language ?

Quote:

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Originally Posted by muke786

but there is already int type to store decimal and float to store float number so what's the specific use of double data type in C language ?

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Precision: float has 24 bits of precision, double has 53 bits of precision, long double has 64 bits of precision.

Anyway... your printf format argument is wrong, it should be "%f". "%Lf" (uppercase ell) is used to 'long double'.

[]s
Fred

Quote:

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Originally Posted by flp1969

your printf format argument is wrong, it should be "%f".

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It's superfluous, but then there's the argument that it is consistent with scanf.

I am not clear I do not understand when to use double data type ?

Nowadays, use double all the time.

floats are a memory space and performance vs range and precision tradeoff back when floating point was done in software (floats are easier to compute with than doubles), and when your entire memory was measured in 10's of KB rather than GB.

Nowadays, most of the systems you'll come across will have floating point hardware and plenty of memory.
Float vs double isn't a choice you need to agonise over.