C :

#include<stdio.h>
#include<string.h>
char a[100];
main()
{
	int i,s=1;
	gets(a);
	for(i=0;i<strlen(a);i++)
	{
		if(a[i]==a[i+1])
		{
			s++;	
		}
		else
		{
			if(s==1)
			{
				printf("%c",a[i]);
			}
			else
			printf("%d%c",s,a[i]);
			s=1;
		}
	}
}

C++ :

#include <iostream>
#include <cstring>
using namespace std;

int main(){
	char a[2000];
	gets(a);
	int i,c = 0;
	for (i = 0;i < strlen(a);i++){
		c++;
		if (i == strlen(a) - 1 || a[i] != a[i + 1]){
			if (c != 1){
				cout<<c<<a[i];
			}else{
				cout<<a[i];
			}
			c = 0;
		}
	}
}

Java :

import java.util.Scanner;
public class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s1 = sc.nextLine();
		s1 = s1 + " ";
		int s = 1;
		for(int i = 0;i < s1.length() - 1;i++){ 
			if(s1.charAt(i) == s1.charAt(i + 1)){
				s++;
			}else{ 
				if(s == 1){
					System.out.print(s1.charAt(i));	
				}else{
					System.out.print(s + "" + s1.charAt(i));
				}
				s = 1;
			}
		}
	}
}

Python :

a = input()
a = a + " "
s= 1
for i in range (0,len(a)-1):
    if a[i]==a[i+1]:
        s += 1
    else:
        if s != 1:
            print(s,end='')
        print(a[i],end='')
        s = 1