Here is source code of the C Program to convert the content of file to UpperCase. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

/*
* C Program to Convert the Content of File to UpperCase
*/
#include <stdio.h>

int to_upper_file(FILE *);

int main(int argc,char *argv[])
{
FILE *fp;
int status;

if (argc == 1)
{
printf("Insufficient Arguments:");
printf("No File name is provided at command line");
return;
}
if (argc > 1)
{
fp = fopen(argv[1],"r+");
status = to_upper_file(fp);

/*
*If the status returned is 0 then the coversion of file content was completed successfully
*/

if (status == 0)
{
printf("\n The content of \"%s\" file was successfully converted to upper case\n",argv[1]);
return;
}
/*
* If the status returnes is -1 then the conversion of file content was not done
*/
if (status == -1)
{
printf("\n Failed to convert");
return;
}
}
}

/*
* convert the file content to uppercase
*/
int to_upper_file(FILE *fp)
{
char ch;

if (fp == NULL)
{
perror("Unable to open file");
return -1;
}
else
{
/*
* Read the file content and convert to uppercase
*/
while (ch != EOF)
{
ch = fgetc(fp);
if ((ch >= 'a') && (ch <= 'z'))
{
ch = ch - 32;
fseek(fp,-1,SEEK_CUR);
fputc(ch,fp);
}
}
return 0;
}
}

/* Input file : mydata
$ cat mydata
This is Manish
I had worked in Wipro and Cisco
*/

$ gcc file3.c
$ a.out mydata
The content of "mydata" file was successfully converted to upper case

/* "mydata" after conversion
$ cat mydata
THIS IS MANISH
I HAD WORKED IN WIPRO AND CISCO
*/