how to generate random number from 0.5 to 1.0

How to Generate the random numb开发者_StackOverflow社区er from 0.5 to 1.0 .

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You can try:

float RandomBetween(float smallNumber, float bigNumber)
{
    float diff = bigNumber - smallNumber;
    return (((float) rand() / RAND_MAX) * diff) + smallNumber;
}

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You should be able to use something like:

double x = ((double)rand()) / ((double)RAND_MAX) / 2.0 + 0.5;

The division by RAND_MAX gives you a value from 0 to 1, dividing that by two drops the range to 0 to 0.5, then adding 0.5 gives you 0.5 to 1. (inclusive at the low end and exclusive at the top end).

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Some thing like bellow will help you.

double random(double start, double end)
{
    double moduleValue = ((end - start) *10); //1.0 - .5 --> .5 -->> 5
    double randum = rand() % moduleValue; // restrict the random to your range
    //if rendum == 2 --> .2 + .5 --> .7 in the range .5 -- 1.0

    return (randum / 10) + start; // make your number to be in your range
}

Test code for clarification

#include <stdio.h>
#define RAND_NUMBER 14
#define INT_FLAG 10
int main (int argc, const char * argv[]) {
    // insert code here...
    double start = .5;
    double end = 1.0;

    double moduleValue = ((end - start) * INT_FLAG);

    int randum = (RAND_NUMBER / moduleValue);

    double result = ((double)randum/INT_FLAG) + start;
    printf("%f",result);
    printf("Hello, World!\n");
    return 0;
}

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#include<stdio.h>
#include<stdlib.h>
main()
{
int i;
double b,n;
srand(getpid());

n=rand()%51+50;
b=n/100;

printf("%f\n",b);
}