Random Function in C

In this topic, we will learn about the random function and how we can generate the random number in the C programming language. As we know, the random function is used to find the random number between any two defined numbers. In the C programming language, the random function has two inbuilt functions: rand() and srand() function. Let’s understand these functions in the C language.

rand() function

In the C programming language, the rand() function is a library function that generates the random number in the range [0, RAND_MAX]. When we use the rand() function in a program, we need to implement the stdlib.h header file because rand() function is defined in the stdlib header file. It does not contain any seed number. Therefore, when we execute the same program again and again, it returns the same values.

Note: If the random numbers are generated with the rand() function without calling the srand() function, it returns the same sequences of numbers each time the program is executed.

Syntax

The rand() function returns the random integers whose range from 0 to RAND_MAX. The RAND_MAX is a symbolic constant that defines in stdlib.h header file, whose value is greater but less than 32767 depending on the C libraries.

Generate the random numbers using the rand() function

Let’s write a program to get the random number using rand() function.

num.c

  #include <stdio.h>  #include <conio.h>  #include <stdlib.h>  void main()  {  // use rand() function to generate the number  printf (” The random number is: %d”, rand());  printf (“n The random number is: %d”, rand());    printf (” n The random number is: %d”, rand());  printf (“n The random number is: %d”, rand());  getch();  }  

Output

The random number is: 41   The random number is: 18467   The random number is: 6334   The random number is: 26500

Generate 5 random numbers using rand() function

Let’s consider a program to generate 5 random number using rand() function in C programming language.

random.c

  #include <stdio.h>  #include <stdlib.h>    int main()  {  int i;  /* It returns the same sequence of random number   on every execution of the program. */  printf(” Random Numbers are: n”);   for (i = 0; i <5; i++)  {  printf(” %d”, rand());   }    return 0;  }  

Output

Random Numbers are:   41 18467 6334 26500 19169

2nd execution of the program:

Random Numbers are:   41 18467 6334 26500 19169

3rd execution of the program

Random Numbers are:   41 18467 6334 26500 19169

As we can see in the above output, it returns the same sequence of random numbers on every execution of the programming code.

Generate 10 random numbers from 1 to 100 using rand() function

Let’s consider a program to find the random number in C using rand() function.

rand_num.c

  #include <stdio.h>  #include <conio.h>  #include <stdlib.h>  int main()  {  // declare the local variables  int i, num;  printf (” Program to get the random number from 1 to 100 n”);  for (i = 1; i <= 10; i++)  {  num = rand() % 100 + 1; // use rand() function to get the random number  printf (” %d “, num);  getch();  }  }  

Output

Program to get the random number from 1 to 100   42  68  35  1  70  25  79  59  63  65

srand() function

The srand() function is a C library function that determines the initial point to generate different series of pseudo-random numbers. A srand() function cannot be used without using a rand() function. The srand() function is required to set the value of the seed only once in a program to generate the different results of random integers before calling the rand() function.

Syntax

seed: It is an integer value that contains a seed for a new sequence of pseudo-random numbers.

Generate the random numbers using srand() function

Let’s write a program to get the random numbers using srand() function in C.

srandNum.c

  #include <stdio.h>  #include <stdlib.h>  #include <time.h> // use time.h header file to use time    int main()  {  int num, i;  time_t t1; // declare time variable    printf(” Enter a number to set the limit for a random number n”);  scanf (” %d”, #);    /* define the random number generator */  srand ( (unsigned) time (&t1)); // pass the srand() parameter  printf(“n”); // print the space  /* generate random number between 0 to 50 */  for (i = 0; i <num; i++)  {  printf( “%d n”, rand() % 50);  }   return 0;  }  

Output

Enter a number to set the limit for a random number  10    44      32      23      35      6       33      1       4       22      18

2nd execution of the program:

Enter a number to set the limit for a random number  15    13      30      24      27      4       30      28      35      36      13      44      39      21      5       7

As we can see in the above Output, it returns different sequences of random numbers on every execution of the programming code.

Generate the random numbers using srand() and time() function

Let’s write a program to get the random numbers using srand() with time() function.

srand_time.c

  #include <stdio.h>  #include <stdlib.h>  int main()  {  int random = rand(); // assign the rand() function to random variable  srand( time(0));    printf( ” Seed = %d”, time(0));  printf( ” Random number = %d”, random);   return 0;  }  

Output

Seed = 1619450091 Random number = 41

Get a seeding value and print the random numbers using srand() function

Let’s write a program to get the seed value and random numbers using srand() function.

srand_time.c

  #include <stdio.h>  #include <stdlib.h>    int main()  {  int count;  unsigned int seed; // use for randomize number    printf(” Enter the Seeding value: n”);  scanf(” %u”, &seed);    srand (seed); // pass parameter    // generate random number between 1 to 6  for (count = 1; count <= 10; ++count)  {  printf(” %5d”, 1 + (rand () % 6));   if (count % 5 == 0) // print the number in next line  puts(” “);   }    return 0;  }  

Output

Enter the Seeding value:  10       6     4     3     3     6       3     3     1     3     4

2nd execution of the program:

Enter the Seeding value:  20       2     4     2     4     5       4     3     5     1     4

3rd execution of the program:

Enter the Seeding value:  25       1     6     1     6     4       4     1     4     1     3

As we can see in the above Output, when we executed the same program again and again with different seeds values, it displays the different sequences of a random number from 1 to 6.

Generate the random number using the random function

Let’s create a program to use stadlib header file to get the random number using random function in C.

func.c

  #include <stdio.h>  #include <conio.h>  #include <stdlib.h>  int main()  {  int i, num, max, temp;  printf (” Enter a number to set the limit of random numbers n”);  scanf (“%d”, num);       printf (” Enter the maximum number from you want to get the random number: n”);  scanf (“%d”, max);     printf (” %d random number from 0 to %d number are: n”, num, max);  randomize();    for (i = 1; i <= num; i++)  {  temp = random(max)  /* use random() function to get the random number */  printf (” %d “, temp); // print the temp  }  getch();  }  

Output

Enter a number to set the limit of random numbers  17  Enter the maximum number from you want to get the random number:  100  15 random number from 0 to 100 number are:   42  68  35  1  70  25  79  59  63  28 75 89 90 43 7 4 65

Program to generate float random numbers

Let’s consider a program to print the float random numbers in C.

random1.c

  #include <stdio.h>  #include <stdlib.h>  #include <time.h>    int main()  {  srand( (unsigned int) time(NULL));  float f1 = 5.0;  int i;  printf(?Float random numbers are: n?);  for (i = 0; i<10; i++)  {  printf(“%f”, ((float) rand()/ RAND_MAX) * f1);  printf(“n”);  }  return 0;  }  

Output

Float random numbers are:  1.208075  1.658376  4.645070  2.298807  3.117161  0.961486  4.115573  4.336223  2.894833  2.249825

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Random Function in C

Random Function in C

rand() function

Note: If the random numbers are generated with the rand() function without calling the srand() function, it returns the same sequences of numbers each time the program is executed.

Syntax

Generate the random numbers using the rand() function

Generate 5 random numbers using rand() function

Generate 10 random numbers from 1 to 100 using rand() function

srand() function

Syntax

Generate the random numbers using srand() function

Generate the random numbers using srand() and time() function

Get a seeding value and print the random numbers using srand() function

Generate the random number using the random function

Program to generate float random numbers

Dangling Pointers in C

Return an Array in C

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