Function 不返回 integer 值 (C)

Question

So I have this code, when I print N it comes out as 0, can someone explain to me why this is happening and how to avoid it?

#include <stdio.h>
#include <math.h>
int enter(char[],int);
int main(void){
    int N,M,i,j,f=1;
    double C=0;
    enter("Enter number N: ",N);
    printf("%d",N);
    return 0;
}
int enter(char s[], int a){
    do{
    printf("%s",s);
    scanf("%d",&a);
    }while(a<1||a>15);
    return a;
}

Answer 1

The signature of enter is confusing: trying to pass it an integer suggests that you want to store the input inside, whereas the integer returned suggests that user should store it.

So the two ways are:

• store input in the given parameter
• return input and store it in a variable

To store inputs in your actual N , use an int* parameter:

enter("Enter number N:", &N); // in main()

void enter(char s[], int* Np) // note void function
{
    // ...
    scanf("%d", Np); // writes input at memory adress of variable N from main()
    // ...
}

To use the value returned by the function to store it in N :

N = enter("Enter N:"); // in main()

int enter(char s[]) // note no integer parameter
{
    int n;
    // ...
    scanf("%d", &n);
    // ...
    return n;
}

Answer 2

You need to save the value returned by the enter function into 'N'

Like this
N = enter("Enter number N: ",N);

Also initialize 'N' to something like N=0, as by default N will be a garbage value.

Or You can pass 'N' by reference instead of value