CODEWITHSUNDEEP
c
apichel
apichel

Reputation: 91

C Function Prototype

Learning C here, and I'm pretty confused on how to use function prototypes.

I'm mainly having a problem calling the function into main. I'm sure I have something messed up in here because all this does is print whatever's in memory.

Thank you for the help.

#include <stdio.h>


double source_volt(double vs);


int main()
{
    double source_volt(double vs);
    double vs;
    printf("%lf", vs);
    return 0;
}


double source_volt(double vs)
{

    int valid = 0;
    do
    {
        printf("Enter source voltage Vs in volts: ");
        scanf("%lf", &vs);

        if (vs < 0 || vs > 100)
        {
            valid = 0;
            printf("Please enter a number between 0 and 100.\n");
        }
        else
            valid = 1;
    }while(!valid);
    return vs;
}

Upvotes: 1

Views: 179

Answers (2)

Brian McFarland
Brian McFarland

Reputation: 9412

The line inside main double source_volt(double vs); actually redeclares the function. And then vs in main is being used without initializing it.

The function source_volt as it's defined would be called like so:

double vs;
vs = source_volt( vs );

However, I'd also like to point out that you're not gaining anything by passing a double into tho function. You could declare a local variable in source_volt and return it to get the same results.

Upvotes: 2

Justin
Justin

Reputation: 2372

This is what is not working for you:

int main()
{
    double source_volt(double vs); //You already declared the function, 
                                   //you dont need the doubles
    double vs;
    printf("%lf", vs);
    return 0;
}

Instead:

int main()
{
    double vs;
    vs = double source_volt(vs); //The double keyword is gone
    printf("%lf", vs);
    return 0;
}

But really, you don't need an argument at all in source volt.

You could rewrite that function to:

double source_volt(void)
{
    double vs;
    int valid = 0;
    do
    {
        printf("Enter source voltage Vs in volts: ");
        scanf("%lf", &vs);

        if (vs < 0 || vs > 100)
        {
            valid = 0;
            printf("Please enter a number between 0 and 100.\n");
        }
        else
            valid = 1;
    }while(!valid);
    return vs;
}

Upvotes: 3

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