What would be the output of the following program ?

main()

{

     const int x = 5; 

      int *ptrx;

      ptrx = &x;

      *ptr = 10;

       printf ("%d", x);

}

Constant expression required in the second case, we cannot use j.

The condition in the while loop is a must.

Here we are initalising the function pointer p to the address of the function fun(). But during this initialisation the function has not been defined. Hence an error.

To eliminate this error add the prototype of the fun() before declaration of p, as shown below:

extern int fun();    or simply  int fun();

Error occurs because we have mixed the ANSI prototype with K & R style of function definition.

When we use ANSI prototype for a function and pass a float to the function it is promoted to a double. When the function accepts this double into a float a type mismatch occurs hence the error.

The remedy for this error could be to define the function as :

int fun (float aa)

{

  ....

}

There is no difference except for the fact that the first one gives a hint that the function fun() is probably in another source file.

extern int i is a declaration and not a definition, hence Error occured.

#include<stdio.h>
int main(){
  FILE *p,*q;
  char file1[20],file2[20];
  char ch;
  printf("\nEnter the source file name to be copied:");
  gets(file1);
  p=fopen(file1,"r");
  if(p==NULL){
      printf("cannot open %s",file1);
      exit(0);
  }
  printf("\nEnter the destination file name:");
  gets(file2);
  q=fopen(file2,"w");
  if(q==NULL){
      printf("cannot open %s",file2);
      exit(0);
  }
  while((ch=getc(p))!=EOF)
      putc(ch,q);
  printf("\nCOMPLETED");
  fclose(p);
  fclose(q);
 return 0;
}

#include<stdio.h>

int main(){

  int a[10][10],i,j,sum=0,m,n;

  printf("\nEnter the row and column of matrix: ");
  scanf("%d %d",&m,&n);

  printf("\nEnter the elements of matrix: ");
  for(i=0;i<m;i++)
      for(j=0;j<n;j++)
           scanf("%d",&a[i][j]);
  printf("\nThe matrix is\n");

  for(i=0;i<m;i++){
      printf("\n");
      for(j=0;j<m;j++){
      printf("%d\t",a[i][j]);
      }
 }
 for(i=0;i<m;i++){
     for(j=0;j<n;j++){
          if(i==j)
              sum=sum+a[i][j];
     }
 }
 printf("\n\nSum of the diagonal elements of a matrix is: %d",sum);

 return 0;
}

Sample output:

Enter the row and column of matrix: 3 3
Enter the elements of matrix:
2
3
5
6
7
9
2
6
7
The matrix is
2       3       5
6       7       9
2       6       7
Sum of the diagonal elements of a matrix is: 16