Write a program in C to count the number of vowels and consonants in a string. You can use fgets to read the characters.

Sure, here is a simple C program that counts the number of vowels and consonants in a string:

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

int main() {
    char str[100];
    int i, vowels = 0, consonants = 0;

    printf("Enter a string: ");
    fgets(str, sizeof(str), stdin);

    for(i = 0; str[i]!='\0'; ++i) {
        if(str[i]=='a' || str[i]=='e' || str[i]=='i' ||
           str[i]=='o' || str[i]=='u' || str[i]=='A' ||
           str[i]=='E' || str[i]=='I' || str[i]=='O' ||
           str[i]=='U') {
            ++vowels;
        }
        else if((str[i]>='a'&& str[i]<='z') || (str[i]>='A'&& str[i]<='Z')) {
            ++consonants;
        }
    }

    printf("Vowels: %d\n", vowels);
    printf("Consonants: %d\n", consonants);

    return 0;
}

This program works by reading a string from the user using fgets(). It then iterates over each character in the string. If the character is a vowel (either lowercase or uppercase), it increments the vowels counter. If the character is a consonant (i.e., it is a letter but not a vowel), it increments the consonants counter. Finally, it prints out the number of vowels and consonants.