how to use negative a number in c language

#include<stdio.h>
int main()
{
    int num;
    printf("Enter a number : ");
     scanf("%d",&num);
     if(num<0)
     {
        printf("Number entered is negative\n");
        num=-num;
     }
     printf("value of num is : %d\n",num);
     return 0;
}