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The following codes does run length encoding and decodes its too...

#include<stdio.h>
void reverseRLE(char *);
void reverse(char *, int , int);
void main()
{
	char ch, s[10000],str[100];
	int i, count = 0, start = 0, end = 0;
	printf("Enter the string \n");
	gets(s);
	ch = s[0];
	i = 1;
	count = 1;
	int j = 0;
	while( s[i] != '\0')
	{
		if(s[i] == ch)
		{   
			//counting no. of occurances
			i++;
			count++;
		}
		else
		{
			//storing the count and the charcter in an array
			printf("%d%c ", count, ch);
			start = j;
			while(count/10 != 0)
			{
				str[j++] = count % 10 + '0';
				count = count/10;
			}
			str[j++] = count + '0';
			end = j-1;
			reverse(str, start, end);
			str[j++] = ch; 
			ch = s[i];
			count = 1;
			i++;
		}
	}
	printf("%d%c ", count, ch);
	if(str[0] != '\0')
	{
		start = j;
		while(count/10 != 0)
		{
			str[j++] = count % 10 + '0';
			count = count/10;
		}
		str[j++] = count + '0';
		end = j-1;
		str[j++] = ch; 		
		str[j] = '\0';	
		reverse(str, start, end);
	}	
	reverseRLE(str);	
}

void reverse(char *s, int start , int end)
{
	int temp = 0;
	while(start < end)
	{
		temp = s[end] - '0';
		s[end] = s[start];
		s[start] = temp + '0';
		start++;
		end--;

	}
}
void reverseRLE(char * s)
{
	int count=0, j = 0, i = 0;
	while(s[i] != '\0')
	{
		if(s[i] > '0' && s[i] < '9')
		{
			count = count*10 + (s[i]-'0');
			j++;
		}
		else
		{
			for(int k =0;k<count;k++)
				printf("%c",s[i]);
			count = 0;
		}
		i++;
	}
	for(int k =0;k<count;k++)
		printf("%c",s[i]);
}

void runLengthEncoding(char s[]){
int count=1, i =0, index = 0,j=0;
int len = strlen(s);
while(i < len){
if(s[i] == s[i+1]){
s[index++] = s[i];
count++;
// index = i + 1;
i++;

while(s[i] == s[++i]){
count++;
}
char p = count + '0';//count is an integer, changing it to character(by adding ASCII value of 0
s[index++] = p;
count =1;
}
else{
s[index++] = s[i++];
}

}
s[index] = '\0';
}

The simplest approach i could think of !!

#include<stdio.h>

int main()
{

float hr, min, angle;

char line[] = "aaabbbbcc";
int i,cnt=1;

for (i=1;i<=strlen(line);i++)
{
if(line[i] == line [i-1])
cnt++;
else
{
printf(" %c %d \n",line[i-1],cnt);
cnt=1;
}
}


return 0;
}

string s;cin>>s;int i=0,l=s.length();
while(i<l)
{
int count=1;
while(i<l && s[i]==s[i+1]){count++;i++;}
cout<<count<<s[i];i++;
}
system("pause");

string s;cin>>s;int i=0,l=s.length();
while(i<l)
{
int count=1;
while(i<l && s[i]==s[i+1]){count++;i++;}
cout<<count<<s[i];i++;
}
system("pause");

Recursive Python version:

def rlencode(s):
    if not s:
        return None
    if len(s) == 1:
        return [[s[0],1]]
    t = rlencode(s[:-1])
    if t[-1][0] != s[-1]:
        return t + [[s[-1],1]]
    t[-1][1] += 1
    return t

def rldecode(code):
    return ''.join(i[1]*i[0] for i in code)

original = 'aaaabbbbbccd'
print('original = ' + original)
encoded = rlencode(original)
print('encoded = ' + str(encoded))
decoded = rldecode(encoded)
print('decoded = ' + decoded)

We can add an "x" and pad all digits (so that its unambigious)

mississippi --> mi2xsi2xsi2xpi
123www -->1x11x21x33xw

code:

string compress_straight(string::iterator cur, string::iterator end) {
  stringstream stream;
  while(cur != end) {
    auto next_char = find_if_not(cur, end, [&](char c) { return c == *cur; });
    int runlen = distance(cur, next_char);
    if (runlen > 1 || isdigit(*cur)) {
      stream << runlen << 'x';
    }
    stream << *cur;
    cur = next_char;
  }
  return stream.str();
}

int main() {
  string word;
  while (true) {
    getline(cin,  word);
    cout << compress_straight(word.begin(), word.end()) << "\n";
  }
}