C Program to Convert the Content of File to Lowercase

This C Program converts the content of file to lowercase.

Here is source code of the C Program to convert the content of file to lowercase. 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 LowerCase

```
 */
```
```
#include <stdio.h>
```
```
#include <errno.h>
```
```
 
```
```
int to_lower_file(FILE *);
```
```
 
```
```
void main(int argc, char * argv[])
```
```
{
```
```
    int op = -1;
```
```
    char ch;
```
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    FILE *fp;
```
```
    if (fp = fopen(argv[1], "r+"))
```
```
    {
```

        printf("FILE has been opened..!!!\n");

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        op = to_lower_file(fp);
```
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        printf(" %d \n", op);
```
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        fclose(fp);
```
```
    }
```
```
    else
```
```
    {
```
```
        perror("Error Occured");
```
```
        printf(" %d\n ", op);
```
```
    }
```
```
}
```
```
 
```
```
int to_lower_file(FILE *f)
```
```
{
```
```
    int c;
```
```
    char ch;
```
```
    while ((ch = fgetc(f))! = EOF)
```
```
    {    
```
```
        c = (int)ch;
```
```
        if (c >= 65 && c <= 90)
```
```
        {
```
```
            ch = ch + 32;
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            fseek(f, -1L, 1);
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            fputc(ch, f);
```
```
        }
```
```
    }
```
```
    return 0;
```
```
}
```

$ gcc file4.c
$ cat test1
THE FUNCTION STRERROR RETURNS A POINTER TO AN ERROR MSG STRING WHOSE CONTENTS ARE IMPLEMENTATION DEFINED.
THE STRING IS NOT MODIFIABLE AND MAYBE OVERWRITTEN BY A SUBSEQUENT CALL TO THE STRERROR FUNCTION.
$ ./a.out test1
FILE has been opened..!!!
 0
$ cat test1
the function strerror returns a pointer to an error msg string whose contents are implementation defined.
the string is not modifiable and maybe overwritten by a subsequent call to the strerror function.

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