While Loop to continually check user input for integer - c

Question

I know this question has been asked before and I am sorry but I cannot find a solution for my code. I am a new student to the C language and my problem is that I am trying to create a while loop that continually asks the user to update the data if they enter non integers. I have looked into the isdigit() function and I think that would work. I just can't seem to make it work for my code, as in whenever I try creating a while loop with isdigit as its condition, I either get a infinite loop, or my isdigit returns values that I was not expecting. I think the problem could be that my scanf() is scanning three integers separated by '/' but I am not sure if that is where the problem is. Any help would be appreciated.
Here is the code in question
#include <stdio.h>
#include <ctype.h>
int calcAge(int a, int b, int c, int d, int e, int f);
int maxHeart(int a);
int heartRangeLow(int a);
int heartRangeHigh(int a);
int main(void) {
int birthMonth = 0, birthDay = 0, birthYear = 0, targetRangeLow = 0;
int month = 0, day = 0, year = 0, age = 0, heartRate = 0, targetRangeHigh = 0;
printf("What is your birthday?(written in MM/DD/YYYY)"
"\nHit Enter after you type it in.\n");
scanf_s("%d/%d/%d", &birthMonth, &birthDay, &birthYear);
printf("What is the date today?(written as MM/DD/YYYY)"
"\nHit Enter after you type it in.\n");
scanf_s("%d/%d/%d", &month, &day, &year);
age = calcAge(birthMonth, birthYear, birthDay, month, day, year);
heartRate = maxHeart(age);
targetRangeLow = heartRangeLow(heartRate);
targetRangeHigh = heartRangeHigh(heartRate);
printf("You are %d years old.\n", age);
printf("Your maximum heart rate is %d beats per minute.\n", heartRate);
printf("Your target-heart-range is %d"
" to %d beats per minute.\n", targetRangeLow, targetRangeHigh);
system("pause");
return 0;
}
int calcAge(int a, int b, int c, int d, int e, int f)
{
int age;
age = ((f * 10000 + d * 100 + e) - (b * 10000 + a * 100 + c)) * .0001;
return age;
}
int maxHeart(int a)
{
int heartRateMax;
heartRateMax = 220 - a;
return heartRateMax;
}
int heartRangeLow(int a)
{
int lowTarget = a * .5;
return lowTarget;
}
int heartRangeHigh(int a)
{
int highTarget = a * .85;
return highTarget;
}

Answer 1

to create a while loop that continually asks the user to update the data if they enter non integers.
Make a helper function.
Read user input with fgets() into a buffer and then parse it for valid input with strtol() or sscanf(), is...(), etc. Return 1, 0, EOF depending on input.
// Untested code
// 1 success
// 0 bad input
// EOF end of file
#define DATE_STR_SIZE 80
int enter_date_mdy(char *prompt, int *m, int *d, int *y) {
if (prompt) {
fputs(prompt, stdout);
fflush(stdout);
}
char buffer[DATE_STR_SIZE];
if (fgets(buffer, sizeof buffer, stdin) == NULL) {
return EOF;
}
int n = 0;
sscanf(buffer, "%d /%d /%d %n", m, d, y, &n);
// If scan incomplete or extra junk at the end ....
if (n == 0 || buffer[n]) {
return 0;
}
// Additional tests as desired ....
if (*m < 1 || *m > 12 || *d < 1 || *d > 31) {
return 0;
}
return 1;
}
Sample use
int count;
do {
count = enter_date_mdy("What is your birthday?(written in MM/DD/YYYY)",
&birthMonth, &birthDay, &birthYear);
if (count == EOF) return(EXIT_FAILURE);
} while (count < 1);
do {
count = enter_date_mdy("What is the date today?(written as MM/DD/YYYY)",
&month, &day, &year);
if (count == EOF) return(EXIT_FAILURE);
} while (count < 1);
Tip: instead of "What is the date today?", research time(), mktime().