Input control(infinite loop problem,c programming) [duplicate]

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
– Paul Ogilvie, Commented Mar 25, 2021 at 15:15
You should add a break statement where you are supposed to exit the loop. — Roberto Caboni
– Roberto Caboni, Commented Mar 25, 2021 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
– Weather Vane, Commented Mar 25, 2021 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
– user15465584, Commented Mar 25, 2021 at 15:26

mkrieger1 · Accepted Answer · 2022-12-13 00:15:53Z

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, 2022 at 0:15

mkrieger1

24.2k7 gold badges68 silver badges84 bronze badges

answered Dec 13, 2022 at 0:13

samaritan

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