C :

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

int main()
{
	int i,n;
	char c,a[201];
	while(scanf("%c%*c%s%*c",&c,a)!=EOF)
	{
		for(n=i=0;i<strlen(a);i++)
			if(c==tolower(a[i])||c==toupper(a[i]))
				n++;
		printf("%.5f\n",n*1.0/strlen(a));
	}
	return 0;
}

C++ :

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

int main()
{
	int i,n;
	char c,a[201];
	while(scanf("%c%*c%s%*c",&c,a)!=EOF)
	{
		for(n=i=0;i<strlen(a);i++)
			if(c==tolower(a[i])||c==toupper(a[i]))
				n++;
		printf("%.5f\n",n*1.0/strlen(a));
	}
	return 0;
}

Java :

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		while(in.hasNext()){
			char c = in.next().charAt(0);
			if(c<='Z')c = (char) (c-'A'+'a');
			String s = in.next();
			int cou = 0;
			for(int i=0;i<s.length();i++){
				char tem = s.charAt(i);
				if(tem<='Z')tem = (char) (tem-'A'+'a');
				if(tem==c)cou++;
			}
				
			System.out.printf("%.5f\n", (float)cou/(float)s.length());
		}
	}

}