Check if a String Contains Only Punctuation Marks in C

To check if a string contains only punctuation marks, iterate through each character and verify if it is a punctuation symbol. In C, you can achieve this using the ispunct() function from <ctype.h> or by manually comparing each character against a set of known punctuation marks.

Example 1: Using ispunct() with a For Loop

In this example, we are going to use the standard library function ispunct() to check if every character in a string is a punctuation mark. We iterate over the string using a for loop.

Program:

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

int main() {
    char str[] = "!@#$%^&*()"; // String containing only punctuation marks
    int flag = 1; // Assume the string is all punctuation

    // Iterate over each character in the string
    for (int i = 0; str[i] != '\0'; i++) {
        if (!ispunct(str[i])) { // Check if character is not a punctuation mark
            flag = 0;
            break;
        }
    }

    if (flag)
        printf("The string contains only punctuation marks.\n");
    else
        printf("The string contains non-punctuation characters.\n");

    return 0;
}

Explanation:

  1. The string str is initialized with punctuation characters.
  2. The variable flag is set to 1, assuming the string is valid.
  3. A for loop iterates through each character of str until the null terminator ('\0') is encountered.
  4. The function ispunct() checks if the current character is a punctuation mark. If not, flag is set to 0 and the loop breaks.
  5. After the loop, the program prints the result based on the value of flag.

Output:

The string contains only punctuation marks.

Example 2: Manual Check Against a List of Punctuation Marks

In this example, we are going to manually check if each character in the string is one of the predefined punctuation marks by using a helper function.

Program:

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

int is_punctuation(char c) {
    // List of common punctuation marks
    char punct[] = "!@#$%^&*()-_+=[]{};:'\",.<>/?\\|`~";
    for (int i = 0; punct[i] != '\0'; i++) {
        if (c == punct[i])
            return 1;
    }
    return 0;
}

int main() {
    char str[] = ".,;:!?"; // String containing only punctuation marks
    int flag = 1;

    // Check each character manually
    for (int i = 0; str[i] != '\0'; i++) {
        if (!is_punctuation(str[i])) {
            flag = 0;
            break;
        }
    }

    if (flag)
        printf("The string contains only punctuation marks.\n");
    else
        printf("The string contains non-punctuation characters.\n");

    return 0;
}

Explanation:

  1. The helper function is_punctuation() checks if a character exists in a predefined string of punctuation marks.
  2. The string str is initialized with punctuation symbols.
  3. A for loop iterates over every character in str.
  4. For each character, the is_punctuation() function is called. If a character is not found in the list, flag is set to 0 and the loop is terminated.
  5. Finally, the program prints whether the string contains only punctuation marks based on the value of flag.

Output:

The string contains only punctuation marks.

Example 3: Using Pointer Arithmetic with ispunct()

In this example, we will use pointer arithmetic to traverse the string and use the ispunct() function to check each character.

Program:

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

int main() {
    char str[] = "!?.,()"; // String containing only punctuation marks
    int flag = 1;
    char *ptr = str; // Pointer to traverse the string

    // Traverse the string using pointer arithmetic
    while (*ptr != '\0') {
        if (!ispunct(*ptr)) {
            flag = 0;
            break;
        }
        ptr++;
    }
    
    if (flag)
        printf("The string contains only punctuation marks.\n");
    else
        printf("The string contains non-punctuation characters.\n");
    
    return 0;
}

Explanation:

  1. The string str is defined with punctuation characters.
  2. A pointer ptr is initialized to point to the beginning of str.
  3. A while loop is used to traverse the string until the null terminator ('\0') is reached.
  4. At each iteration, the character pointed to by ptr is checked with ispunct(). If it is not a punctuation mark, flag is set to 0 and the loop is exited.
  5. After the loop, the result is printed based on the value of flag.

Output:

The string contains only punctuation marks.

Conclusion

In this tutorial, we explored multiple approaches to verify if a string contains only punctuation marks in C. We used the built-in ispunct() function with both a for loop and pointer arithmetic, as well as a manual method with a helper function to compare each character against a predefined list of punctuation symbols.