#include<stdio.h>
int main()
{
char line[150];
int i, j;
printf("Enter a string: ");
gets(line);
for(i = 0; line[i] != '\0'; ++i)
{
while (!( (line[i] >= 'a' && line[i] <= 'z') || (line[i] >= 'A' && line[i] <= 'Z') || line[i] == '\0') )
{
for(j = i; line[j] != '\0'; ++j)
{
line[j] = line[j+1];
}
line[j] = '\0';
}
}
printf("Output String: ");
puts(line);
return 0;
}

This program takes a string from the user and stored it in the variable line.

, within the for loop, each character in the string is checked if it’s an alphabet or not.

If any character inside a string is not an alphabet, all characters after it including the null character shifted by 1 position to the left

C program to remove all characters in a string except alphabets:

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

int main() {
    char str[100], new_str[100];
    int i, j = 0;

    printf("Enter a string:\n");
    gets(str);

    for (i = 0; i < strlen(str); i++) {
        if (isalpha(str[i])) {
            new_str[j] = str[i];
            j++;
        }
    }

    new_str[j] = '\0';

    printf("Original string: %s\n", str);
    printf("String with only alphabets: %s\n", new_str);

    return 0;
}

Explanation:

• #include <stdio.h>, #include <string.h> and #include <ctype.h> include the standard input-output, string, and character functions header files respectively in our program.
• char str[100], new_str[100]; declares two character arrays str and new_str to store the original and modified strings respectively.
• int i, j = 0; declares two loop variables i and j.
• The printf() the statement is used to display a message to the user to input a string and the gets() function is used to input the string.
• The for the loop starting from for (i = 0; i < strlen(str); i++) checking each character in the string str using the isalpha() function, which returns true if the character is an alphabet. If the character is an alphabet, it is added to the new_str array and the index is incremented.
• The statement new_str[j] = '\0'; adds the null character at the end of the modified string to indicate the end of the string.
• The last printf() the statement displays the original and modified strings.

When we compile and run this program, it will prompt the user to input a string and then remove all characters except alphabets. Finally, it will display both the original and modified strings.