How to generate a random int in C?

Question

Is there a function to generate a random int number in C? Or will I have to use a third party library?

Answer 1

Try this, I put it together from some of the concepts already referenced above:

/*    
Uses the srand() function to seed the random number generator based on time value,
then returns an integer in the range 1 to max. Call this with random(n) where n is an integer, and you get an integer as a return value.
 */

int random(int max) {
    srand((unsigned) time(NULL));
    return (rand() % max) + 1;
}

Answer 2

This is a good way to get a random number between two numbers of your choice.

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

    #define randnum(min, max) \
        ((rand() % (int)(((max) + 1) - (min))) + (min))

int main()
{
    srand(time(NULL));

    printf("%d\n", randnum(1, 70));
}

Output the first time: 39

Output the second time: 61

Output the third time: 65

You can change the values after randnum to whatever numbers you choose, and it will generate a random number for you between those two numbers.

Answer 3

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

//generate number in range [min,max)
int random(int min, int max){
    int number = min + rand() % (max - min);
    return number; 
}

//Driver code
int main(){
    srand(time(NULL));
    for(int i = 1; i <= 10; i++){
        printf("%d\t", random(10, 100));
    }
    return 0;
}