...
#include <string.h>
...
char string[100];
fgets(string, sizeof(string), stdin);
// use the following to get rid of the newline character
// that gets attached to the end of the input string
string[strcspn(string, "\n")] = '\0';
...

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

void concatenateStrings(char str1[], char str2[], char result[]) {
    int i = 0, j = 0;

    // Copy first string into result
    while (str1[i] != '\0') {
        result[i] = str1[i];
        i++;
    }

    // Append second string to result
    while (str2[j] != '\0') {
        result[i] = str2[j];
        i++;
        j++;
    }
    result[i] = '\0'; // Null-terminate the result string
}

int main() {
    char str1[100], str2[100], result[200];

    printf("Enter the first string: ");
    fgets(str1, sizeof(str1), stdin);
    str1[strcspn(str1, "\n")] = '\0'; // Remove newline character

    printf("Enter the second string: ");
    fgets(str2, sizeof(str2), stdin);
    str2[strcspn(str2, "\n")] = '\0'; // Remove newline character

    concatenateStrings(str1, str2, result);

    printf("Concatenated string: %s\n", result);

    return 0;
}

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

int stringLength(char str[]) {
    int length = 0;
    while (str[length] != '\0') {
        length++;
    }
    return length;
}

int main() {
    char str[100];

    printf("Enter a string: ");
    fgets(str, sizeof(str), stdin);
    str[strcspn(str, "\n")] = '\0'; // Remove newline character

    int length = stringLength(str);
    printf("The length of the string is: %d\n", length);

    return 0;
}

...
#include <ctype.h>
...
// The value of ch after running the following statement is 'A'
char ch = toupper('a');
...

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

int main() {
    char str[100];

    printf("Enter a string: ");
    fgets(str, sizeof(str), stdin);
    str[strcspn(str, "\n")] = 0; // Remove newline character

    for (int i = 0; str[i] != '\0'; i++) {
        str[i] = toupper(str[i]); // Convert to uppercase
    }

    printf("String in uppercase: %s\n", str);

    return 0;
}

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

int findFirstOccurrence(char str[], char ch) {
    for (int i = 0; str[i] != '\0'; i++) {
        if (str[i] == ch) {
            return i; // Return the index of the first occurrence
        }
    }
    return -1; // Return -1 if the character is not found
}

int main() {
    char str[100], ch;

    printf("Enter a string: ");
    fgets(str, sizeof(str), stdin);
    str[strcspn(str, "\n")] = '\0'; // Remove newline character

    printf("Enter the character to find: ");
    scanf("%c", &ch);

    int index = findFirstOccurrence(str, ch);

    if (index != -1) {
        printf("The first occurrence of '%c' is at index %d.\n", ch, index);
    } else {
        printf("Character not found in the string.\n");
    }

    return 0;
}

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

int countOccurrences(char str[], char ch) {
    int count = 0;
    for (int i = 0; str[i] != '\0'; i++) {
        if (str[i] == ch) {
            count++;
        }
    }
    return count;
}

int main() {
    char str[100], ch;

    printf("Enter a string: ");
    fgets(str, sizeof(str), stdin);
    str[strcspn(str, "\n")] = '\0'; // Remove newline character

    printf("Enter the character to count: ");
    scanf("%c", &ch);

    int count = countOccurrences(str, ch);

    printf("The character '%c' appears %d times in the string.\n", ch, count);

    return 0;
}