This program takes a number from the user and checks whether that number is either positive or negative or zero.

Check Positive or Negative Using if…else

#include <stdio.h>
int main(){
    double num;
    printf("Enter a number: ");
    scanf("%lf", &num);
    if (num <= 0.0) {
        if (num == 0.0)
            printf("You entered 0.");
        else
            printf("You entered a negative number.");
    } else
        printf("You entered a positive number.");
    return 0;
}

You can also solve this problem using nested if else statement.

Check Positive or Negative Using Nested if…else

#include <stdio.h>
int main(){
    double num;
    printf("Enter a number: ");
    scanf("%lf", &num);

    if (num < 0.0)
        printf("You entered a negative number.");
    else if (num > 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.