How to do it…

1. Open the sequential file in read-only mode using the following code:

fp = fopen (argv [1],"r");

2. If the file does not exist or does not have enough permissions, an error message will be displayed and the program will terminate, as shown in the following code:

if (fp == NULL) {
    printf("%s file does not exist\n", argv[1]);
    exit(1);
 }

3. Initialize the counter that will count the number of vowels in the file to 0, as shown in the following code:

count=0;

4. One line is read from the file, as shown in the following code:

fgets(buffer, BUFFSIZE, fp);

5. Each character of the line is accessed and checked for any lowercase or uppercase vowels, as shown in the following code:

if(buffer[i]=='a' || buffer[i]=='e' || buffer[i]=='i' || buffer[i]=='o' || buffer[i]=='u' || buffer[i]=='A' || buffer[i]=='E' || buffer[i]=='I' || buffer[i]=='O' || buffer[i]=='U')

6. If any vowel is found, the value of the counter is incremented by 1, as shown in the following code:

count++;

7. Step 5 will be repeated until the end of the line has been reached. Check whether the end of the file has been reached. Repeat from step 4 until the end of the file, as shown in the following code:

while (!feof(fp))

8. Display the count of the number of vowels in the file by printing the value in the counter variable on the screen, as shown in the following code:

printf("The number of vowels are %d\n",count);

The preceding steps are shown in the following diagram:

Figure 5.3

The countvowels.c program to count the number of vowels in a sequential text file is as follows:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define BUFFSIZE 255

void main (int argc, char* argv[])
{
    FILE *fp;
    char buffer[BUFFSIZE];
    int n, i, count=0;
    fp = fopen (argv [1],"r");
    if (fp == NULL) {
        printf("%s file does not exist\n", argv[1]);
        exit(1);
    }
    printf("The file content is :\n");
    while (!feof(fp))
    {
        fgets(buffer, BUFFSIZE, fp);
        puts(buffer);
        n=strlen(buffer);
        for(i=0;i<n;i++)
        {
            if(buffer[i]=='a' || buffer[i]=='e' || buffer[i]=='i' || 
            buffer[i]=='o' || buffer[i]=='u' || buffer[i]=='A' || 
            buffer[i]=='E' || buffer[i]=='I' || buffer[i]=='O' || 
            buffer[i]=='U') count++;
        }         
    }
    printf("The number of vowels are %d\n",count);
    fclose(fp);
}

Now, let's go behind the scenes.