Question

How to convert an integer into its written‑out English words in C

Answer 1

#include <stdio.h>
#include <string.h>
 
static const char *below20[] = {
    "", "one", "two", "three", "four", "five", "six", "seven",
    "eight", "nine", "ten", "eleven", "twelve", "thirteen",
    "fourteen", "fifteen", "sixteen", "seventeen", "eighteen",
    "nineteen"
};
 
static const char *tens[] = {
    "", "", "twenty", "thirty", "forty", "fifty",
    "sixty", "seventy", "eighty", "ninety"
};
 
void append(char *buf, const char *word) {
    if (word && *word) {
        strcat(buf, word);
        strcat(buf, " ");
    }
}
 
void setBelow20AndTens(int num, char *buf) {
    if (num == 0) return;
 
    if (num < 20) {
        append(buf, below20[num]);
    } else if (num < 100) {
        append(buf, tens[num / 10]);
        setBelow20AndTens(num % 10, buf);
    } else {
        append(buf, below20[num / 100]);
        append(buf, "hundred");
        setBelow20AndTens(num % 100, buf);
    }
}
 
void numberToWords(int num, char *buf) {
    buf[0] = '\0';  // clear buffer
 
    if (num == 0) {
        strcpy(buf, "zero");
        return;
    }
 
    if (num >= 1000000000) {
        setBelow20AndTens(num / 1000000000, buf);
        append(buf, "billion");
        num %= 1000000000;
    }
    if (num >= 1000000) {
        setBelow20AndTens(num / 1000000, buf);
        append(buf, "million");
        num %= 1000000;
    }
    if (num >= 1000) {
        setBelow20AndTens(num / 1000, buf);
        append(buf, "thousand");
        num %= 1000;
    }
    if (num > 0) {
        setBelow20AndTens(num, buf);
    }
 
    // Trim trailing space
    int len = strlen(buf);
    if (len > 0 && buf[len - 1] == ' ')
        buf[len - 1] = '\0';
}
 
int main(void) {
    int n = 176283;
    char buffer[256] = "";
 
    numberToWords(n, buffer);

    printf("%s\n", buffer);
 
    return 0;
}
 
 
 
/*
run:
 
one hundred seventy six thousand two hundred eighty three
 
*/

 

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