Input control(infinite loop problem,c programming)

Question

I keep getting values as long as the user does not enter a positive integer (and I control if user entered negative values or if user entered an integer). I try to do it without using isdigit, it enters an infinite loop when I enter a character.

int quantity;
        
printf("Please enter term(s) number");
scanf("%d",&quantity);
while( 1){
    if(quantity<0){
        printf("Please enter “positive”  number");
        scanf("%d",&quantity);
    }

    if(!(quantity>='0' && quantity<='9')){
        printf("Please enter “a”  number");
        scanf("%d",&quantity);
    }
}

You read an integer. Then `quantity>='0'` will always be false (`'0'` means ASCII character 0) — Paul Ogilvie, Mar 25 '21 at 15:15
You should add a `break` statement where you are supposed to exit the loop. — Roberto Caboni, Mar 25 '21 at 15:15
The 'character' is presumably non-numeric. This blocks the input until you remove it. One easier way to deal with this to use `fgets()` for all input and then `sscanf()` and then, if `sscanf()` returns the wrong value, or the entry is the wrong value, you dump the string and ask for another.. — Weather Vane, Mar 25 '21 at 15:20
@PaulOgilvie while( ( !(quantity>='0' && quantity<='9')) || quantity<0) when i use this and enter a character there is still infinite loop,ı dont know how to solve it — user15465584, Mar 25 '21 at 15:26
@RobertoCaboni If user provides a positive integer (not a character or a negative integer) I want to exit and I typed this way which part should I edit — user15465584, Mar 25 '21 at 15:30
@WeatherVane honestly i don't use anything but scanf because homework — user15465584, Mar 25 '21 at 15:31
Please see [How to clear input buffer in C?](https://stackoverflow.com/questions/7898215/how-to-clear-input-buffer-in-c) Particularly [this answer](https://stackoverflow.com/a/26081123/4142924). That means you will use `getchar()` but you can find a way to do it with `scanf()` too. — Weather Vane, Mar 25 '21 at 15:36
@WeatherVane Thank you very much, that was the problem, solved.if you can type this an answer i can approve it,i dont know another way to close the session*/ — user15465584, Mar 25 '21 at 15:51

score 1 · Accepted Answer · edited Dec 13 '22 at 00:15

1

Use fgets() to get an entire line. You use strtol() to parse the line as an integer, checking if it consumed the entire line.

char *end;
char buf[LINE_MAX];

do {
     if (!fgets(buf, sizeof buf, stdin))
        break;

     // remove \n
     buf[strlen(buf) - 1] = 0;

     int n = strtol(buf, &end, 10);
} while (end != buf + strlen(buf));

edited Dec 13 '22 at 00:15

mkrieger1

19,194
5
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answered Dec 13 '22 at 00:13

samaritan

74
9

Input control(infinite loop problem,c programming)

1 Answers1