CODEWITHSUNDEEP
cclion
bothge
bothge

Reputation: 17

How to make user input correctly

The question is about the part of code you can see below. I have two variables leftLimit and rightLimit. Their values should strictly be from -1 to 1 (not included). Ok, I solved this problem. When the input is >= than |1| program will ask until needed value is input. But it only works when input has digital value. When input is a or / and so on, I get the end of program and nothing works. How can I fix it? How to prevent my program from non-digital input?

#include <stdio.h>
#include <math.h>
int main() {
double leftLimit, rightLimit;
printf("Enter the left limit: ");
scanf ("%lf", &leftLimit);
while (fabs(leftLimit)>=1) {                
    printf("\nYou typed a wrong limit, try again: ");
    scanf("%lf", &leftLimit);
}
printf("\nEnter the right limit: ");
scanf("%lf", &rightLimit);


while (fabs(rightLimit)>=1) {                 
    printf("\nYou typed a wrong limit, try again: ");
    scanf("%lf", &rightLimit);
}

Upvotes: 0

Views: 90

Answers (1)

pmg
pmg

Reputation: 108978

scanf() is ill-suited for user input. Prefer fgets() possibly followed by sscanf() or strtol() or strtod()

double leftLimit;
char buffer[1000];
for (;;) {
    printf("Enter left limit: ");
    fflush(stdout);
    if (!fgets(buffer, sizeof buffer, stdin)) exit(EXIT_FAILURE);
    char *err;
    leftLimit = strtod(buffer, &err);
    if (*err != '\n') continue;
    if (fabs(leftLimit) >= 1) continue;
    break; // all ok
}
printf("Accepted left limit of %f.\n", leftLimit);

Upvotes: 1

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