Floating-point format specifiers control how floating-point values are formatted by printf(). The conversion specifier determines the notation, while the precision controls the number of digits displayed after the decimal point for %f-style output.

#include <stdio.h>

int main()
{
    float a = 3.14159f;
    double b = 1234.5678;
    long double c = 3.141592653589793L;

    printf("float       : %f\n", a);
    printf("double      : %.3f\n", b);
    printf("long double : %.15Lf\n", c);

    printf("Scientific  : %e\n", b);
    printf("General     : %g\n", b);

    return 0;
}

Example Output #

float       : 3.141590
double      : 1234.568
long double : 3.141592653589793
Scientific  : 1.234568e+03
General     : 1234.568

Explanation #

The %f conversion displays a floating-point value using decimal notation:

printf("%f\n", a);

The precision can be specified using .n:

printf("%.3f\n", b);

Here, 3 specifies three digits after the decimal point.

Floating-Point Format Specifiers #

Precision #

For %f, precision specifies the number of digits after the decimal point:

printf("%.2f\n", 3.14159);

Output:

3.14

For %e and %E, precision specifies the number of digits after the decimal point in the mantissa.

For %g and %G, precision specifies the number of significant digits, and trailing zeros are normally removed.

A float argument passed to printf() is automatically promoted to double, so %f is used for both float and double arguments. For long double, the L length modifier is required.