# Difference between float and double in C/C++

For representing floating point numbers, we use **float**, **double** and **long double**.

**What’s the difference ?**

**double** has 2x more precision then **float**.

**float** is a 32 bit IEEE 754 single precision Floating Point Number1 bit for the sign, (8 bits for the exponent, and 23* for the value), i.e. float has 7 decimal digits of precision.

**double** is a 64 bit IEEE 754 double precision Floating Point Number (1 bit for the sign, 11 bits for the exponent, and 52* bits for the value), i.e. double has 15 decimal digits of precision.

Let’s take a example(example taken from here) :

For a quadratic equation **x2 – 4.0000000 x + 3.9999999 = 0**, the exact roots to 10 significant digits are, r1 = 2.000316228 and r2 = 1.999683772

`// C program to demonstrate ` `// double and float precision values` ` ` `#include <stdio.h>` `#include <math.h>` ` ` `// utility function which calculate roots of ` `// quadratic equation using double values` `void` `double_solve(` `double` `a, ` `double` `b, ` `double` `c){` ` ` `double` `d = b*b - 4.0*a*c;` ` ` `double` `sd = ` `sqrt` `(d);` ` ` `double` `r1 = (-b + sd) / (2.0*a);` ` ` `double` `r2 = (-b - sd) / (2.0*a);` ` ` `printf` `(` `"%.5f\t%.5f\n"` `, r1, r2);` `}` ` ` `// utility function which calculate roots of ` `// quadratic equation using float values` `void` `float_solve(` `float` `a, ` `float` `b, ` `float` `c){` ` ` `float` `d = b*b - 4.0f*a*c;` ` ` `float` `sd = sqrtf(d);` ` ` `float` `r1 = (-b + sd) / (2.0f*a);` ` ` `float` `r2 = (-b - sd) / (2.0f*a);` ` ` `printf` `(` `"%.5f\t%.5f\n"` `, r1, r2);` `} ` ` ` `// driver program` `int` `main(){` ` ` `float` `fa = 1.0f;` ` ` `float` `fb = -4.0000000f;` ` ` `float` `fc = 3.9999999f;` ` ` `double` `da = 1.0;` ` ` `double` `db = -4.0000000;` ` ` `double` `dc = 3.9999999;` ` ` ` ` `printf` `(` `"roots of equation x2 - 4.0000000 x + 3.9999999 = 0 are : \n"` `);` ` ` `printf` `(` `"for float values: \n"` `);` ` ` `float_solve(fa, fb, fc);` ` ` ` ` `printf` `(` `"for double values: \n"` `);` ` ` `double_solve(da, db, dc);` ` ` `return` `0;` `} ` |

Output:

roots of equation x2 - 4.0000000 x + 3.9999999 = 0 are : for float values: 2.00000 2.00000 for double values: 2.00032 1.99968

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