Dividing 1/n always returns 0.0 [duplicate]

问题

This question already has answers here:

C program to convert Fahrenheit to Celsius always prints zero (8 answers)

Why does division result in zero instead of a decimal? (5 answers)

Closed last year.

I am trying to calculate p1=(1/1)*(1/2)*...*(1/n) but something is wrong and the printf gives me 0.000...0

#include <stdio.h>

int main(void) {

    int i,num;
    float p3;

    do {
        printf ("give number N>3 : \n" );
        scanf( "%d", &num );
    } while( num <= 3 );

    i = 1;
    p3 = 1;  

    do {
        p3=p3*(1/i);
        printf( "%f\n",p3 );
    } while ( i <= num );

    printf("\nP3=%f",p3);
    return 0;
}

回答1:

(1/i)

i is an int, so that's integer division, resulting in 0 if i > 1. Use 1.0/i to get floating point division.

回答2:

1 is an integer, i is an integer. So 1/i will be an integer, ie the result will be truncated. To perform floating-point division, one of the operands shall be of type float (or, better, of type double):

p3 *= 1. / i;

回答3:

I had the same issue. The basic case:

• when you want to get float output from two integers, you need to convert one into float

  int c = 15; int b = 8; printf("result is float %f\n", c / (float) b); // result is float 1.875000 printf("result is float %f\n", (float) c / b); // result is float 1.875000

来源：https://stackoverflow.com/questions/13331054/dividing-1-n-always-returns-0-0