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>

using namespace std;

int main(){

    string msg;
    cin >> msg;
    msg += " ";
    char tmp = msg[0];
    int count = 1;
    string encode = "";

    for(int i=1;i<msg.size();i++){
        if (msg[i]==tmp)
            count ++;
        else{
            if (count!=1)
                cout << char( count+'0' );
            cout << tmp;
            tmp = msg[i];
            count = 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