# 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
```

This article is contributed by Mandeep Singh. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

# GATE CS Corner    Company Wise Coding Practice

Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.
2 Average Difficulty : 2/5.0
Based on 3 vote(s)