How to create C program to determine lagest number by entered value? - c

Question

I've created a program to determine largest number, but my lecturer says it isn't perfect, can anybody make it perfect?
#include <stdio.h>
int main () {
double a,b=0,n, i;
printf("limit of n input: ");
scanf ("%lf",&n);
for (i=1;i<=n;i++) {
scanf("%lf",&a);
if (a>b) b=a;
}
printf("%.2lf", b);
return 0;
}

Answer 1

If by "not perfect" she meant "doesn't properly handle negative numbers or an empty set", then you'd want to
Treat n<1 as a special case (why should 0 be the largest of an empty set?)
Read the first number outside of the loop, so you're not making as assumption as to the smallest possible number

Answer 2

I would do it that way, sorry for the mass of text. I think it is coming from the typical Objective-C style programming with long words:
#include <stdio.h>
int clean_stdin() {
while (getchar()!='\n');
return 1;
}
int main(int argc, char *argv[]) {
char c;
signed int count = 0; // number of numbers to scan
unsigned int fireErrorMessage = 0;
do {
if (fireErrorMessage == 1) {
printf("You entered not a positive natural number. Please enter a number >0 Examples: 1 22 4012\n"); // output for the user
}
if (fireErrorMessage == 0) {
fireErrorMessage = 1;
}
printf("How many integers do you want to insert (Inser a number >0)? ");
} while (((scanf("%d%c", &count, &c) != 2 || c != '\n') && clean_stdin()) || count < 1);
signed int indexOfNumber; // for index, declared outside because of output at the end
signed int highestNumberIndex;
double highestNumber; // saving the highest value in a helper variable
fireErrorMessage = 0;
for (indexOfNumber = 1; indexOfNumber <= count; indexOfNumber++) {
double scannedNumber;
do {
if (fireErrorMessage == 1) {
printf("You entered not a number. Please enter a number. Examples: 3.0 -1 14\n"); // output for the user
}
if (fireErrorMessage == 0) {
fireErrorMessage = 1;
}
printf("Input number %d: ", indexOfNumber); // output for the user
} while (((scanf("%lf%c", &scannedNumber, &c) != 2 || c != '\n') && clean_stdin()));
fireErrorMessage = 0;
if (indexOfNumber == 1 || scannedNumber > highestNumber) {
highestNumberIndex = indexOfNumber;
highestNumber = scannedNumber;
}
}
printf("Highest input number on index %d, the value is about %.2lf\n", highestNumberIndex, highestNumber);
return 0;
}
Output
How many integers do you want to insert (Inser a number >0)? aa5
You entered not a positive natural number. Please enter a number >0 Examples: 1 22 4012
How many integers do you want to insert (Inser a number >0)? -3
You entered not a positive natural number. Please enter a number >0 Examples: 1 22 4012
How many integers do you want to insert (Inser a number >0)? 3
Input number 1: aa
You entered not a number. Please enter a number. Examples: 3.0 -1 14
Input number 1: -50.0001
Input number 2: 51a
You entered not a number. Please enter a number. Examples: 3.0 -1 14
Input number 2: -1.00
Input number 3: -0.1
Highest input number on index 3, the value is about -0.10

Answer 3

This code caters for negative, not a number input for the loop index as well as negative and not a number inputs inside the loop. Thanks
#include <stdio.h>
#include <math.h>
int main () {
int n, i;
double a,b=0;
printf("limit of n input: ");
scanf ("%lf",&n);
if(n < 0){
printf("value of n cannot be negative");
return 0;
}
else if (n == 0)
return 0;
else if (isnan(n))
return 0;
else{
for (i=1;i<=n;i++)
{
scanf("%lf",&a);
if(!isnan(a) && a > 0)
{
if (a>b) b=a;
}
}
printf("%.2lf", b);
return 0;
}
}