C Getting decimal input from user issue -

i'm trying write function decimal input user , return actual value converted ascii. however, function causes next input user skipped. in:
enter input: 123

enter input: /* doesn; allow input */

enter input: 456

long sum = 0;  int character = fgetc(stdin);  while(character != '\n'){      if(character >= '0' && character <= '9'){         /* convert ascii */         character -= '0';         sum = sum * 10 + character;      }     else{         /* reenter number */     }     character = fgetc(stdin); } return sum; 

to figure out why code doesn't work, suggest post full code, because problems may lie in way call function.

so before full code posted, can tell code works on machine:

#include <stdio.h> #include <ctype.h>  int getlong();  int main() {     printf("\t%d\n", getlong());     printf("\t%d\n", getlong());     return 0; }  int getlong() {     long sum = 0;     int character = fgetc(stdin);     while (character != '\n') {         if (isdigit(character)) {             /* convert ascii */             character -= '0';             sum = sum * 10 + character;             character = fgetc(stdin);         }         else {             character = fgetc(stdin);             continue;         }     }     return sum; } 

ctype.h included in order use isdigit(), while tells whether character decimal digit.

but in fact, don't have on own. using standard library more effective , efficient, both , computer.

for example, can scan long integer directly stdin:

#include <stdio.h>  int main() {     long value;     puts("please input numbers:");     while (scanf(" %ld", &value) != 1) {         puts("only numbers welcome:");         scanf("%*[^\n]");     }     printf("%ld", value);     return 0; } 

notice white-space @ beginning of format, makes scanf() discard white-space characters(including spaces, newline , tab characters) extracted until non-white-space character met.

or, use strtol(), while relatively seen:

#include <stdio.h> #include <stdlib.h>  int main() {     char buf[80];     char *pend;     long value;         {         puts("numbers please:");         if (fgets(buf, 80, stdin) == null)         {             perror("fgets()");             return 1;         }         value = strtol(buf, &pend, 10);     }     while (*pend != '\n');     printf("%ld", value);     return 0; } 

of course, sscanf() works, can write code on own.