Find char in string and print it's position from left and right

#include<stdio.h>
#include<conio.h>
void main()
{
    int len=0,i,pos,flag;
    char a[100],c;
    clrscr();
    printf("Enter string");
    gets(a);
    printf("Enter charactor to match");
    scanf("%c",&c);
    for(len=0;a[len]!=NULL;len++);
    for(i=0;i<len;i++)
    {

        if(a[i]==c)
        {
            pos=i;
            flag=0;
        }
    }
    if(flag==0)
    {
        printf("%c is matched",c);
        printf("\nit is at %d possition from left",pos+1);
        printf("\nit is at %d possition from right ",len-pos);
    }
    else
    printf("Not matched");
    getch();
}