C program to replace first occurrence of vowel with ‘-‘ in string

In this tutorial, we will learn how to write a C program to replace the first occurrence of vowel with ‘-‘.

C Program to replace first occurrence of vowel in a String with ‘-‘

Let’s write the code. The detailed explanation of the program is provided at the end of the code. The brief explanation is provided in the program itself using comments.

#include <stdio.h>

// Function to replace the first occurrence of a vowel with '-'
void replaceFirstVowel(char str[]) {
    //String that contains lowercase and uppercase vowels
    //We will use this to check the vowels in input string
    char vowels[] = "aeiouAEIOU"; 
    int i, j;
    
    // Traverse the string to find the first vowel
    for (i = 0; str[i] != '\0'; i++) {
        for (j = 0; vowels[j] != '\0'; j++) {
            if (str[i] == vowels[j]) {
                str[i] = '-'; // Replace the first vowel with '-'
                return; // Exit the function after replacing
            }
        }
    }
}

int main() {
    char str[100]; // Array to hold input string
    
    // Prompt the user to enter a string
    printf("Enter a string: ");

    // Read the input string and store in array str[]
    fgets(str, sizeof(str), stdin); 
    
    // Remove newline character if present
    int len = 0;
    while (str[len] != '\0') {
        if (str[len] == '\n') {
            str[len] = '\0';
            break;
        }
        len++;
    }
    
    // Call the function to replace the first vowel
    replaceFirstVowel(str);
    
    // Print the modified string
    printf("Modified string: %s\n", str);
    
    return 0;
}

Output:

Output 1:

Enter a string: Hello World
Modified string: H-llo World

Output 2:

Enter a string: PINK
Modified string: P-NK

Output 3:

Enter a string: Hey!
Modified string: H-y!

Explanation of the program:

replaceFirstVowel() Function:

void replaceFirstVowel(char str[]) {
    char vowels[] = "aeiouAEIOU"; 
    int i, j;
    
    for (i = 0; str[i] != '\0'; i++) {
        for (j = 0; vowels[j] != '\0'; j++) {
            if (str[i] == vowels[j]) {
                str[i] = '-'; // Replace the first vowel with '-'
                return; // Exit the function after replacing
            }
        }
    }
}

• In this function, we have an array vowels that contains lowercase and uppercase vowels.
• It returns nested for loop, to check whether any of the input string character matches with the any element of vowels array.
• When a vowel is found, it is replaced with '-', and the function exits immediately.

main() Function:

• In main function, we prompts the user to enter a string using printf function.
• It uses fgets to read the input string and store it into array str[].
• The program removes the newline from the input string
• It calls the replaceFirstVowel() function to replace the first vowel with '-'.
• Finally, it prints the modified string.