#include<stdio.h>

int main(){

  int a[3][3],i,j;

  long determinant;



  printf("Enter the 9 elements of matrix: ");
  for(i=0;i<3;i++)
      for(j=0;j<3;j++)
           scanf("%d",&a[i][j]);

  printf("\nThe matrix is\n");
  for(i=0;i<3;i++){
      printf("\n");
      for(j=0;j<3;j++)
           printf("%d\t",a[i][j]);
  }

  determinant = a[0][0]*((a[1][1]*a[2][2]) - (a[2][1]*a[1][2])) -a[0][1]*(a[1][0]*a[2][2] - a[2][0]*a[1][2]) + a[0][2]*(a[1][0]*a[2][1] - a[2][0]*a[1][1]);

  printf("\nDeterminant of 3X3 matrix: %ld",determinant);
 
   return 0;
}
Sample output:
Enter the 9 elements of matrix: 1
2
3
4
5
6
7
8
9

The matrix is

1       2       3
4       5       6
7       8       9

Determinant of 3X3 matrix: 0

#include<stdio.h>
int main(){
FILE *fp;
char ch;
fp=fopen("file.txt","w");
printf("\nEnter data to be stored in to the file:");
while((ch=getchar())!=EOF)
putc(ch,fp);
fclose(fp);
return 0;
}

#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(){
    FILE *p;
    char ch;
    p=fopen("raja.c","r");
    while((ch=getc(p))!=-1)
         putchar(ch);
    fclose(p);
    return 0;
}

#include<stdio.h>
int main(){
char str[70];
FILE *p;
if((p=fopen("string.txt","r"))==NULL){
printf("\nUnable t open file string.txt");
exit(1);
}
while(fgets(str,70,p)!=NULL)
puts(str);
fclose(p);
return 0;
}