C programming

[automat]

Hello.
I need some help, please. 
Thank you.

1. To mirror the numbers in a two-dimensional array. For instance for a number, if the number is : 2345, and the number in mirror is 5432.

#include<stdio.h>
#include<math.h>
#define matrix [20][20]
#define matrix1 [20][20]
void main()
{
   int number_lines, number_columns, i, j, ogl, nr;
   printf("\n Give the number of lines : ");
   scanf("%ld", &number_lines);
   printf("\n Give the number of columns : ");
   scanf("%ld", &number_columns);
   printf("\n Give the elements of matrix : ");
   printf("\n");
   for(i=1; i<=number_lines; i++) 
      {
        for(j=1; j<=number_columns; j++)  
            {
               printf("\n Matrix [%d][%d] = ", i, j);
               scanf("%d", &nr);
               matrix1[i][j] = matrix[i][j];
            }
      }
   for(i=1; i<=number_lines; i++)  
       {
          for(j=1; j<=number_columns; j++)  
              {
                 ogl = 0;
                 while(matrix[i][j] != 0)
                    {
                        ogl = ogl * 10 + matrix[i][j] % 10;
                        matrix[i][j] = matrix[i][j] / 10;
                    }
        printf("\n The mirror of matrix[%d][%d] --> %d is %d\n", i, j, matrix1[i][j], ogl);
        }
    }
}


2. To carry out a program to display prime numbers from a given range. 

#include<stdio.h> 
void main() 
{ 
    int a, b, prime, d, i; 
    printf("\n Give a = "); 
    scanf("%d", &a); 
    printf("\n Give b = "); 
    scanf("%d", &b); 
    if(b<=a) 
    printf("\n b must be greather than a.\n"); 
    prime=1; d=2; 
      for(i=a; i<=b; i++) 
          { 
              while(d<=i/2 && prime) 
                    { 
                        if(i%d==0) 
                        prime=0; 
                        d++; 
                    } 
             if(prime) 
               printf(" %d", i); 
             else 
               printf("\n No prime in the interval [%d %d].\n", a, b); 
         } 
   }

[camel-man]

Remember that void main() is not accepted on this forum lol make it int main() and return 0 at the bottom another thing is remember that your arrays start at 0 you have your for loops starting at 1 so you will be skipping the actual first column and row when inputting

[anduril462]

Good effort with the code tags, but you missed the mark a bit. Use one set of code tags for each problem/program. Don't put your assignment description, questions, etc in code tags.

It's int main(void) and return 0; at the end. Read this link.


The following are for your mirror program:

• You don't declare a 2-d array (or any array) with #define. Read our array tutorial and Google for some more. Crack open that textbook too.
• Read the scanf documentation. %ld is for long integers. You want %d for regular ints.
• Arrays in C go from 0 to size-1, so for a 20x20 matrix, the highest indexes are [19][19]. You should use for (i = 0; i < size; i++) for your array processing loops.
• You scanf into nr, but don't do anything with nr. You then copy from matrix (which is uninitialized and full of garbage) into matrix1.
• After that, you reverse the garbage numbers in matrix, and print out the unreversed matrix1.

This is for your prime program:

• You need to set prime to 1 every time that while loop runs. Same thing with setting d = 2.
• You need a separate variable to track if there were any primes whatsoever in the interval.
• If that separate variable is true, print "No primes..." only once, after your for loop is done.