C program to write all digits into words using for loop

In C programming, converting digits to their word equivalents is a common task that helps beginners understand conditional statements and loops. This program takes a range of digits and prints each digit as its corresponding word using a for loop.

Syntax

for(initialization; condition; increment) {
    // Convert digit to word using if-else statements
}

Example: Converting Digits to Words in a Range

This example demonstrates how to convert all digits from 3 to 8 into their word representations using a for loop −

#include <stdio.h>

void digitToWord(int digit) {
    if(digit < 0 || digit > 9) {
        printf("Beyond range of 0 - 9");
    } else if(digit == 0) {
        printf("Zero");
    } else if(digit == 1) {
        printf("One");
    } else if(digit == 2) {
        printf("Two");
    } else if(digit == 3) {
        printf("Three");
    } else if(digit == 4) {
        printf("Four");
    } else if(digit == 5) {
        printf("Five");
    } else if(digit == 6) {
        printf("Six");
    } else if(digit == 7) {
        printf("Seven");
    } else if(digit == 8) {
        printf("Eight");
    } else if(digit == 9) {
        printf("Nine");
    }
}

int main() {
    int start = 3, end = 8;
    
    printf("Converting digits %d to %d into words:<br>", start, end);
    
    for(int i = start; i <= end; i++) {
        digitToWord(i);
        printf("<br>");
    }
    
    return 0;
}

Converting digits 3 to 8 into words:
Three
Four
Five
Six
Seven
Eight

Example: Using Array-Based Approach

A more efficient approach uses an array to store digit words, eliminating multiple if-else conditions −

#include <stdio.h>

int main() {
    char *digitWords[] = {"Zero", "One", "Two", "Three", "Four", 
                         "Five", "Six", "Seven", "Eight", "Nine"};
    int start = 3, end = 8;
    
    printf("Using array approach:<br>");
    
    for(int i = start; i <= end; i++) {
        if(i >= 0 && i <= 9) {
            printf("%s<br>", digitWords[i]);
        } else {
            printf("Invalid digit<br>");
        }
    }
    
    return 0;
}

Using array approach:
Three
Four
Five
Six
Seven
Eight

Key Points

• The if-else ladder approach is beginner-friendly but verbose for larger ranges.
• The array approach is more efficient and scalable with O(1) lookup time.
• Always validate input to ensure digits are within the valid range (0-9).
• The for loop iterates through the specified range, calling the conversion function for each digit.

Conclusion

Converting digits to words using a for loop demonstrates fundamental programming concepts like loops, conditional statements, and functions. The array-based approach provides a cleaner and more maintainable solution for digit-to-word conversion.