#include <stdio.h>
int main()
{
char str[1000], ch;
int i, frequency = 0;
printf("Enter a string: ");
gets(str);
printf("Enter a character to find the frequency: ");
scanf("%c",&ch);
for(i = 0; str[i] != '\0'; ++i)
{
if(ch == str[i])
++frequency;
}
printf("Frequency of %c = %d", ch, frequency);
return 0;
}

Output

Enter a string: This website is awesome.
Enter a character to find the frequency: e
Frequency of e = 4

In this program, the string entered by the user is stored in variable str.

Then, the user is asked to enter the character whose frequency is to be found. This is stored in variable ch.

Now, using the for loop, each character in the string is checked for the entered character.

If, the character is found, the frequency is increased. If not, the loop continues.

Finally, the frequency is printed.

a step-by-step explanation of a C program that finds the frequency of characters in a given string:

#include <stdio.h>
#include <string.h>

#define MAX_SIZE 100 // define a macro to represent the maximum size of the string

int main() {
    char str[MAX_SIZE];
    int freq[256] = {0}; // initialize a frequency array with all elements set to 0
    int i, len;

    printf("Enter a string: ");
    fgets(str, sizeof(str), stdin); // read a line of text from the standard input stream

    len = strlen(str); // get the length of the string

    for (i = 0; i < len; ++i) { // loop through each character in the string
        ++freq[str[i]]; // increment the frequency of the current character
    }

    printf("Frequency of characters in the string:\n");

    for (i = 0; i < 256; ++i) { // loop through each character code (ASCII code)
        if (freq[i] != 0) { // check if the frequency of the current character is not 0
            printf("'%c' occurs %d times\n", i, freq[i]); // print the character and its frequency
        }
    }

    return 0; // indicate successful completion of the program
}

Let’s break it down step-by-step:

1. We include the necessary header files: stdio.h for input/output functions and string.h for string handling functions.

2. We define a macro MAX_SIZE to represent the maximum size of the string.

3. We declare a character array str of size MAX_SIZE to hold the input string, an integer array freq of size 256 to store the frequency of each character, and integer variables i and len.

4. We prompt the user to enter a string using printf(), and read a line of text from the standard input stream using fgets(), which takes in three arguments: the character array to store the input, the size of the array, and the input stream (in this case, stdin for standard input).

5. We get the length of the string using strlen(), which returns the number of characters in the string (excluding the null terminator).

6. We use a for loop to iterate through each character in the string. The loop runs from i = 0 to i < len, where len is the length of the string.

7. Inside the loop, we use ++freq[str[i]] to increment the frequency of the current character. This uses the ASCII code of the character as the index of the freq array.

8. Once the loop is complete, we use printf() to print the frequency of each character in the string. We use another for loop to iterate through each character code (ASCII code), and check if the frequency of the current character is not 0. If it is not 0, we print the character and its frequency using printf().

9. Finally, we return 0 to indicate successful completion of the program.