Count Common characters in two strings

Given two strings, count total number of common characters. For example if two strings are "coder" and "side" then common characters are 2 ( 'd' and 'e' ). If strings are "Programming" and "Side" then common character is 'i'. If strings are "aabbcc" and "aabcc" then common characters are 5 ( 2'a', 1'b', 2'c' ).

Simple method is create a character count array for string 1 and count frequency of each characters in string and then count common characters in string 2. If strings are "aabbccab" and "aabd". And a variable to count common characters is common_char = 0.

count frequency of each character in string 1
count['a'] = 3;
count['b'] = 3;
count['c'] = 2;

Now find common characters in string 2.

str2[0] => count['a'] = 3;  common_char = 1;  count['a']--;
str2[1] => count['a'] = 2;  common_char = 2;  count['a']--;
str2[2] => count['b'] = 3;  common_char = 3; count['b']--;
str2[3] => count['d'] = 0;  common_char = 3; count['d'] (no change)

C Program:

/* Count common characters in two string */
#include<stdio.h>
#include<stdlib.h>
#define MAX 256
 
int *CountArray(char *str)
{
 int *count=(int *)calloc(sizeof(int),MAX);
 int i; 

/* Count frequency of each character in first string */ 

 for(i=0;*(str+i);i++)
 {
  count[*(str+i)]++;
 }
 return count;
}
 
int CountCommonChar(char *str1, char *str2)
{
 int *count=CountArray(str1);
 int i,count_char=0;
 for(i=0;*(str2+i);i++)
 {
  if(count[*(str2+i)]!=0)
  {
   count_char++;
   count[*(str2+i)]--;
  }
 }
 
 return count_char;
}
int main()
{
 char str1[100],str2[100];
 
 printf("Enter first string: ");
 scanf("%s",str1);
 printf("Enter second string: ");
 scanf("%s",str2);
 
 int n=CountCommonChar(str1,str2);
 printf("Common char = %d",n);
 
 return 0;
}