Float and Double in C

In C programming, float and double are data types used to represent floating point numbers. Both follow the IEEE 754 standard but differ in precision and memory usage.

Float Data Type

Float is a 32-bit IEEE 754 single precision floating point number with the following structure −

• 1 bit for the sign
• 8 bits for the exponent
• 23 bits for the mantissa (fractional part)
• Precision: 6-7 decimal digits

Syntax

float variable_name;

Example: Float Declaration and Usage

#include <stdio.h>

int main() {
    float x = 10.327f;
    int y = 28;
    
    printf("The float value: %.6f
", x);
    printf("The sum of float and int: %.6f
", (x + y));
    
    return 0;
}

The float value: 10.327000
The sum of float and int: 38.327000

Double Data Type

Double is a 64-bit IEEE 754 double precision floating point number with the following structure −

• 1 bit for the sign
• 11 bits for the exponent
• 52 bits for the mantissa
• Precision: 15-17 decimal digits

Syntax

double variable_name;

Example: Double Declaration and Usage

#include <stdio.h>

int main() {
    float x = 10.327f;
    double y = 4244.546789123456;
    int z = 28;
    
    printf("The float value: %.6f
", x);
    printf("The double value: %.15lf
", y);
    printf("The sum of all variables: %.6f
", (x + y + z));
    
    return 0;
}

The float value: 10.327000
The double value: 4244.546789123456000
The sum of all variables: 4282.873789

Comparison

Conclusion

Use float when memory is a concern and moderate precision is sufficient. Choose double for applications requiring high precision calculations, as it provides nearly twice the precision of float with minimal performance overhead on modern systems.