Here is source code of the C Program to replace a specified line in a text file. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

/*
* C Program to Replace a specified Line in a Text File
*/
#include <stdio.h>

int main(void)
{
FILE *fileptr1, *fileptr2;
char filechar[40];
char c;
int delete_line, temp = 1;

printf("Enter file name: ");
scanf("%s", filechar);
fileptr1 = fopen(filechar, "r");
c = getc(fileptr1);
//print the contents of file .
while (c != EOF)
{
printf("%c", c);
c = getc(fileptr1);
}
printf(" \n Enter line number to be deleted and replaced");
scanf("%d", &delete_line);
//take fileptr1 to start point.
rewind(fileptr1);
//open replica.c in write mode
fileptr2 = fopen("replica.c", "w");
c = getc(fileptr1);
while (c != EOF)
{
if (c == 'n')
{
temp++;
}
//till the line to be deleted comes,copy the content to other
if (temp != delete_line)
{
putc(c, fileptr2);
}
else
{
while ((c = getc(fileptr1)) != 'n')
{
}
//read and skip the line ask for new text
printf("Enter new text");
//flush the input stream
fflush(stdin);
putc('n', fileptr2);
//put 'n' in new file
while ((c = getchar()) != 'n')
putc(c, fileptr2);
//take the data from user and place it in new file
fputs("n", fileptr2);
temp++;
}
//continue this till EOF is encountered
c = getc(fileptr1);
}
fclose(fileptr1);
fclose(fileptr2);
remove(filechar);
rename("replica.c", filechar);
fileptr1 = fopen(filechar, "r");
//reads the character from file
c = getc(fileptr1);
//until last character of file is encountered
while (c != EOF)
{
printf("%c", c);
//all characters are printed
c = getc(fileptr1);
}
fclose(fileptr1);
return 0;
}




$ cc pgm48.c
$ a.out
Enter file name: pgm3.c
/*
* C Program to Convert Octal to Decimal
*/

#include <stdio.h>
#include <math.h>

int main()
{

long int octal, decimal = 0;
int i = 0;

printf("Enter any octal number: ");
scanf("%ld", &octal);
while (octal != 0)
{
decimal = decimal +(octal % 10)* pow(8, i++);
octal = octal / 10;
}
printf("Equivalent decimal value: %ld",decimal);
return 0;
}

Enter line number to be deleted and replaced 13 replaced
Enter new text
/*
* C Program to Convert Octal to Decimal
*/

#include <stdio.h>
#include <math.h>

int main()
{

long int octal, decimal = 0;
int i = 0;
replaced
printf("Enter any octal number: ");
scanf("%ld", &octal);
while (octal != 0)
{
decimal = decimal +(octal % 10)* pow(8, i++);
octal = octal / 10;
}
printf("Equivalent decimal value: %ld",decimal);
return 0;
}