program to count the number of vowels in a string

program to count the number of vowels in  a string
#include<stdio.h>
struct student
{
char name[25];
int roll;
int marks;
};
void main()
{
struct student s1[100];
int n,i;
printf("Enter the no. of students you want to evaluate the data for:");
scanf("%d",&n);
printf("\n\n");
for(i=0;i<n;i++)
{
printf("DATA FOR STUDENT:%d",(i+1));
printf("\n\nEnter Name:");
scanf("%s",&s1[i].name);
printf("\nEnter Roll:");
scanf("%d",&s1[i].roll);
printf("\nEnter Marks:");
scanf("%d",&s1[i].marks);
printf("\n");
}
printf("STUDENTS DETAILS:\n");
for(i=0;i<n;i++)
{
printf("\nName:%s\n",s1[i].name);
printf("Roll number:%d\n",s1[i].roll);
printf("Total mark:%d\n",s1[i].marks);
}
printf("\n\n");
printf("Students who got above 75:\n");
for(i=0;i<n;i++)
{
if(s1[i].marks>75)
{
printf("Studentno.%d,%s,%d",(i+1),s1[i].name,s1[i].marks);
}
printf("\n");
}
}