C Exercises: Generates 50 random numbers between -0.5 and 0.5

Last update on March 18 2025 13:30:17 (UTC/GMT +8 hours)

Generate 50 random numbers in [-0.5, 0.5] and save them to a file

Write a C program that generates 50 random numbers between -0.5 and 0.5 and writes them to the file rand.dat. The first line of ran.dat contains the number of random numbers, while the next 50 lines contain 50 random numbers.

Sample Solution:

C Code:

#include <stdio.h> 
#include <stdlib.h> 
#include <time.h> 
#define N 50
int main() {
  int i;
  char str;
  FILE * fptr;
  
  // Open a file for writing
  fptr = fopen("rand.dat", "w");
  if (fptr == NULL) {
    printf("Error in creating output.dat\n");
    return 0;
  }

  // Seed the random number generator
  srand(time(NULL));
  
  // Write the number of values to the file
  fprintf(fptr, "%d\n", N);
  
  // Generate and write random numbers to the file
  for (i = 1; i <= N; i++) {
    fprintf(fptr, "%0.4lf\n", (rand() % 2001 - 1000) / 2.e3);
  }
  
  // Close the file
  fclose(fptr);
  
  // Open the file for reading
  fptr = fopen ("rand.dat", "r");  
  str = fgetc(fptr);
  
  // Print the contents of the file
  while (str != EOF)
  {
    printf ("%c", str);
    str = fgetc(fptr);
  }
  
  // Close the file
  fclose(fptr);
  
  return 0;
}

Sample Output:

50
-0.4215
0.2620
0.3065
-0.0485
-0.2085
-0.2490
-0.2780
0.2905
-0.3120
0.1275
0.4010
0.3060
0.4680
-0.1135
0.0130
-0.0145
-0.1890
-0.3825
0.3790
-0.2370
0.0840
-0.1985
0.2065
0.4445
0.0785
-0.2370
-0.0705
0.3870
-0.4695
0.1525
0.2755
0.3880
-0.3075
-0.1400
-0.3825
-0.0155
-0.1105
-0.1605
-0.4470
0.0780
0.4675
0.2330
-0.3380
0.2135
0.3980
0.1750
0.4780
-0.2915
0.0715
0.3565

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C program to generate 100 random floating-point numbers in the range [-1, 1] and save them to a file.
• Write a C program to generate random numbers within a user-specified range and write them to a binary file.
• Write a C program to generate 50 random numbers in a given range, sort them, and then write them to a file.
• Write a C program to generate random numbers in [-0.5, 0.5], compute their average, and write both to a file.

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