find occurrences of each character in string in c in O(n) code example

Example: Write a c program to count the different types of characters in given string.

#include<stdio.h>
   #include<string.h> 
	void main()    {
   		char arr[]="askjdfbajksdfkasdfhjkasdfh";
   		char x;
   		int l=strlen(arr);
   		int i=0,j;
   		int c=0,var=0;
   		for(j=97;j<=122;j++) {     //a=97,z=122
   		//c=j;           
   			for(i=0;i<l-1;i++) {
   	       		if(arr[i]==j) {
   	         		c++; 
   	       		} 
   	     	} 
   	  		if(c>0) {
   	    		var++;
   	    		printf("No. of Occurence of %c ::%d\n",j,c); 
   	  		}
   	  		c=0; 
   		} 
   	  	printf("No. of type of characters:%d\n",var);   
   	}