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Generating random number in a range in C

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  • Difficulty Level : Easy
  • Last Updated : 24 Aug, 2022
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How to generate a random number in a given range in C. Examples:

Input : Lower = 50,
        Upper = 100,
        Count of random Number = 5 
Output : 91 34 21 88 29 
Explanation: lower is the lower limit of the 
range and upper is the upper limit of the range.
Output contains 5 random numbers in given range.

C does not have an inbuilt function for generating a number in the range, but it does have rand function which generates a random number from 0 to RAND_MAX. With the help of rand () a number in range can be generated as num = (rand() % (upper – lower + 1)) + lower 

C




// C program for generating a
// random number in a given range.
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
 
// Generates and prints 'count' random
// numbers in range [lower, upper].
void printRandoms(int lower, int upper,
                            int count)
{
    int i;
    for (i = 0; i < count; i++) {
        int num = (rand() %
        (upper - lower + 1)) + lower;
        printf("%d ", num);
    }
}
 
// Driver code
int main()
{
    int lower = 5, upper = 7, count = 1;
 
    // Use current time as
    // seed for random generator
    srand(time(0));
 
    printRandoms(lower, upper, count);
 
    return 0;
}

Output:

7

Time complexity: O(N) where N is the count of random numbers to be generated

Auxiliary Space: O(1)

Note: Output generated on each run may be different because the number is generated randomly.

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