Write a C Program to count the frequency of each character

Follow the algorithm to write a C program which enables to count the frequency of each character.

Algorithm

Step 1: Define MAX size.
Step 2: Declare char and integer variables.
Step 3: Read the string from console.
Step 4: Find length of the string.
Step 5: Initialize frequency of each character to 0.
Step 6: Find total number of occurrences of each character.
for(i=0; i<length; i++)
   i. if(string[i]>='a' && string[i]<='z')
   frequency[string[i] - 97]++;
   ii. else if(string[i]>='A' && string[i]<='Z')
      frequency[string[i] - 65]++;
Step 7: Print the frequency of all characters in the string.
if(frequency[i] != 0)
   printf("'%c' = %d\n", (i + 97), frequency[i]);

Example

Given below is the C program to count frequency of each character in a string −

#include <stdio.h>
#include <string.h>
#define MAX 100 // Maximum string size
int main(){
   char string[MAX];
   int i, length;
   int frequency[20];
   /* Input string from user */
   printf("enter the string:\n ");
   gets(string);
   length = strlen(string);
   /* Initialize frequency of each character to 0 */
   for(i=0; i<20; i++){
      frequency[i] = 0;
   }
   /* Find total number of occurrences of each character */
   for(i=0; i<length; i++){
      /* If the current character is lowercase alphabet */
      if(string[i]>='a' && string[i]<='z'){
         frequency[string[i] - 97]++;
      }
      else if(string[i]>='A' && string[i]<='Z'){
         frequency[string[i] - 65]++;
      }
   }
   /* Print the frequency of all characters in the string */
   printf("\nFrequency of all characters in string: \n");
   for(i=0; i<20; i++){
      /* If current character exists in given string */
      if(frequency[i] != 0){
         printf("'%c' = %d\n", (i + 97), frequency[i]);
      }
   }
   return 0;
}

Output

When the above program is executed, it produces the following result −

enter the string:
Tutorials Point
Frequency of all characters in string:
'a' = 1
'i' = 2
'l' = 1
'n' = 1
'o' = 2
'p' = 1
'r' = 1
's' = 1
't' = 3