PROGRAM-1:
Check if a number is positive or negative using if...else
#include <stdio.h>
int main()
{
    double number;
 
    printf("Enter a number: ");
    scanf("%lf", &number);
 
    if (number <= 0.0)
    {
        if (number == 0.0)
            printf("You entered 0.");
        else
            printf("You entered a negative number.");
    }
    else
        printf("You entered a positive number.");
    return 0;
}
 
PROGRAM-2: 
Check if a number is positive or negative using nested if...else
#include <stdio.h>
int main()
{
    double number;
 
    printf("Enter a number: ");
    scanf("%lf", &number);
    if (number < 0.0)
        printf("You entered a negative number.");
    else if ( number > 0.0)
        printf("You entered a positive number.");
 
    else
        printf("You entered 0.");
    return 0;
}
 
OUTPUT-1:
Enter a number: 12.3
You entered a positive number.
 
OUTPUT-2:
Enter a number: 0
You entered 0.