formatting a number

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

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):

Code:

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

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

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

Code:

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#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);
}

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Thanks to the both of you