Count Vowels in a String

CSC-115 · Semester I · C Programming

beginner20 minAvailable

Cin-browser interpreter · runs locally

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

int main() {
  char s[64] = "hello world";
  int vowels = 0;
  for (int i = 0; i < strlen(s); i++) {
    char c = s[i];
    if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u' ||
        c == 'A' || c == 'E' || c == 'I' || c == 'O' || c == 'U') {
      vowels++;
    }
  }
  printf("Vowels in %s = %d\n", s, vowels);
  return 0;
}

17 lines

Output

Write some code, then press Run. Stdout and errors appear here.

Lab brief

Objective

Read a string, traverse it with strlen, and count how many characters are vowels (a, e, i, o, u).

Theory & concepts

A string is a char array ending in '\0'. Looping from index 0 to strlen(s) - 1 visits every character. For each character, test whether it matches a, e, i, o, or u (in both cases) and increment a counter.

Rendering diagram…

Traversing a string to count vowels

for (int i = 0; s[i] != '\0'; i++) {
    char c = tolower(s[i]);
    if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u')
        count++;
}

The loop condition s[i] != '\0' stops exactly at the end of the string, whether it was typed or read from a file. tolower (from ctype.h) folds upper-case vowels into lower case so one set of comparisons covers both.

Prerequisites

Lesson: Strings and string functions
Lesson: String input and output

Instructions

1Declare a char array and read a line with fgets.
2Loop over the string while s[i] != '\0'.
3Check each character for a, e, i, o, u in lower and upper case.
4Increment a vowel counter for every match.
5Print the total vowel count and verify against a known string.

Tasks

Count the vowels
Input 'hello world' - the count must be 3 (e, o, o).
Handle upper case
Input 'AeIoU' - the count must be 5.
Count consonants too
Extend the program to also print the number of consonants.
Count each vowel separately
Track a, e, i, o, u in five counters and report each one.

Self-check

Vowel counts are correct for mixed-case strings.
The loop terminates on the null character.
Non-letter characters such as spaces and digits do not inflate the count.
The student can explain why the string ends at '\0'.

Environment

editorstandard inputstdout consoletest cases