• Source 
    1. #include <stdio.h>
    2. #include <conio.h>
    3. #include <string.h>
    4. #include <stdlib.h>
    5.  
    6. #define SIZE 100
    7. char *tens(int n);
    8. char *hundred(int n);
    9.  
    10. int main(){
    11.     char *p,*ptr,*temp;
    12.     long n;
    13.     int a,flag=0,c=0;
    14.     char t[][10]={"Thousand","Million","Billion","Trillion"};
    15.  
    16.     p=(char *) malloc(SIZE * sizeof(char));                      
    17.     temp=(char *) malloc(SIZE * sizeof(char));
    18.     printf("\nEnter a number : ");
    19.     scanf(" %ld",&n);
    20.     if(n<1000){
    21.                ptr=hundred(n);
    22.                strcpy(p,ptr);
    23.                free(ptr);
    24.     } else {
    25.            a=n%1000;
    26.            ptr=hundred(a);
    27.            strcpy(p,ptr);
    28.            free(ptr);
    29.            n=n/1000;
    30.            while (n>0){
    31.                 a=(n>999)? n%1000 : n;
    32.                 ptr=hundred(a);
    33.                 strcpy(temp,ptr);
    34.                 strcat(temp," ");
    35.                 strcat(temp,t[c++]);
    36.                 strcat(temp," ");
    37.                 strcat(temp,p);
    38.                 free(p);
    39.                 p=(char *) malloc(SIZE * sizeof(char));                      
    40.                 strcpy(p,temp);
    41.                 free(temp);
    42.                 temp=(char *) malloc(SIZE * sizeof(char));
    43.                 free(ptr);
    44.                 n=n/1000;
    45.            }
    46.     }
    47.     printf("\n %s",p);
    48.     free(p);
    49.     getch();  
    50. }
    51.  
    52. char *tens(int n){
    53.      int a;
    54.      char *p,temp[20];
    55.      char t1[][10]={"Zero","One","Two","Three","Four","Five","Six","Seven","Eight","Nine","Ten",
    56.                   "Eleven","Twelve","Thirteen","Fourteen","Fifteen","Sixteen","Seventeen","Eighteen","Nineteen"};
    57.      char t2[][10]={"Twenty","Thirty","Forty","Fifty","Sixty","Seventy","Eighty","Ninety"};
    58.  
    59.      if(n<20){
    60.               strcpy(temp,t1[n]);
    61.      } else {
    62.             a=n/10-2; 
    63.             strcpy(temp,t2[a]);
    64.             if((a=n%10)!=0) { 
    65.                             strcat(temp," ");  
    66.                             strcat(temp,t1[a]); 
    67.             }
    68.      }
    69.  
    70.      p=(char *) malloc((strlen(temp)+1)*sizeof(char));
    71.      strcpy(p,temp);
    72.      return(p);
    73. }
    74.  
    75. char *hundred(int n){
    76.      int a;
    77.      char temp[40],*p;
    78.      char t[][10]={"Zero","One","Two","Three","Four","Five","Six","Seven","Eight","Nine"};
    79.  
    80.      if(n>99 && n<1000){
    81.               a=n/100;
    82.               strcpy(temp,t[a]);
    83.               strcat(temp," Hundred ");
    84.               a=n%100;
    85.  
    86.               p=tens(a);
    87.               strcat(temp,p);
    88.               free(p);
    89.      } else {
    90.             p=tens(n);
    91.             strcpy(temp,p);
    92.             free(p);
    93.      }
    94.               p=(char *) malloc((strlen(temp)+1)*sizeof(char));
    95.               strcpy(p,temp);
    96.               return(p);
    97. }
    98.