Count spaces, uppercase and lowercase in a sentence using C

In C programming, counting different types of characters in a string is a common task. This involves analyzing each character to determine if it's uppercase, lowercase, a digit, whitespace, or a special character.

Syntax

for (int i = 0; str[i] != '\0'; i++) {
    // Check character type using ASCII values
    if (str[i] >= 'A' && str[i] <= 'Z')      // Uppercase
    else if (str[i] >= 'a' && str[i] <= 'z') // Lowercase
    else if (str[i] >= '0' && str[i] <= '9') // Digits
    else if (str[i] == ' ')                // Whitespace
}

Example: Character Classification

This example demonstrates how to count spaces, uppercase letters, lowercase letters, digits, and special characters in a string −

#include <stdio.h>

int main() {
    char str[100];
    int upper = 0, lower = 0, digits = 0, spaces = 0, special = 0;
    
    printf("Enter a string: ");
    fgets(str, sizeof(str), stdin);
    
    for (int i = 0; str[i] != '\0'; i++) {
        if (str[i] >= 'A' && str[i] <= 'Z') {
            upper++;
        }
        else if (str[i] >= 'a' && str[i] <= 'z') {
            lower++;
        }
        else if (str[i] >= '0' && str[i] <= '9') {
            digits++;
        }
        else if (str[i] == ' ') {
            spaces++;
        }
        else if (str[i] != '
') {
            special++;
        }
    }
    
    printf("Uppercase letters: %d
", upper);
    printf("Lowercase letters: %d
", lower);
    printf("Digits: %d
", digits);
    printf("Spaces: %d
", spaces);
    printf("Special characters: %d
", special);
    
    return 0;
}

Enter a string: Hello World 123!
Uppercase letters: 2
Lowercase letters: 8
Digits: 3
Spaces: 1
Special characters: 1

Key Points

• We use fgets() instead of gets() for safer input handling.
• ASCII value ranges: 'A'-'Z' (65-90), 'a'-'z' (97-122), '0'-'9' (48-57).
• The condition str[i] != '
' excludes the newline character from special characters.
• Each character is checked sequentially using if-else conditions.

Conclusion

Character classification in C uses ASCII value comparisons to categorize each character in a string. This technique is essential for text processing and input validation in C programs.