formatting a number

[Allanon]

Hi,
How can I take a number like 3.243434 and format it so that the returned value is 3.24
Thanks

[parksie]

A quick and dirty solution is to multiply it by 10^(number of decimal places), cast to an integer, then cast back to a float and divide by 10^(number of decimal places). However, this will fall over on accurate conversion, since it will merely truncate rather than use the last digit correctly. So, you need to add 5 * 10^(-places):

float num = 3.46564;
int places = 2;
float pow10 = pow(10, places);

num = (float)((long)(num * pow10));
num += 5 * (1.0f / pow10);
num /= pow10;

I think...you'd have to test it

[KingDavid]

#include <stdio.h> 
#include <stdlib.h> 

double fNum(double n,unsigned int places);
float fNum(float n,unsigned int places);

void main()
{
	double d = 83.010903;
	double dFormated;

	float f = 123.456f;

	// Double's
	// print the number
	printf("%f \n",d);

	// print the number formated
	printf("%.1f \n",d);
	printf("%.2f \n",d);
	printf("%.3f \n",d);
	printf("%.4f \n",d);
	printf("%.5f \n",d);

	// format the number
	dFormated = fNum(d,5);
	printf("%f \n",dFormated);

	// Floats
	printf("%f \n",f);
	f = fNum(f,2);
	printf("%f \n",f);
}

double fNum(double n,unsigned int places)
{
	int  decimal, sign;
	char b[20]; // buffer	
	char *e; //extra

	_ecvt(n,places,&decimal,&sign);//get the number digits before Decimal point
	char * s = _gcvt(n, decimal + places, b); // convert it to string	
	n = strtod(s,&e);
	
	
	return (n);// convert it to double and return
	// when the number is returned it adds zeros on the end,
	// I don't know why it does this!
}

float fNum(float n,unsigned int places)
{
	// same thing but floats!
	int  decimal, sign;
	char b[20];
	char *e; 

	_ecvt(n,places,&decimal,&sign);
	char * s = _gcvt(n, decimal + places, b);
	n = (float)strtod(s,&e);	
	
	return (n);
}

[Allanon]

Thanks to the both of you