Sum of 2 numbers

Hi everyone. I am trying to do a simple program in C which reads two double numbers from the keyboard and displays the sum to the user. Even though the compiling is ok, the program doesn't run as expected. The code is:

Code:

#include <stdio.h>

int main (void)
{

    double num1, num2, sum;

    printf("Type in the first number: ");
    scanf("%f", &num1);
    printf("Type in the second number: ");
    scanf("%f", &num2);

    sum = num1 + num2;

    printf("%f + %f = %f.", num1, num2, sum);

    return 0;

}

What is wrong with this code?

Thanks in advance!

You need a compiler which warns you when you get printf/scanf wrong.

Eg.

Code:

$ gcc bar.c
bar.c: In function ‘main’:
bar.c:9: warning: format ‘%f’ expects type ‘float *’, but argument 2 has type ‘double *’
bar.c:11: warning: format ‘%f’ expects type ‘float *’, but argument 2 has type ‘double *’
$ gcc bar.c
$ ./a.out 
Type in the first number: 123
Type in the second number: 456
123.000000 + 456.000000 = 579.000000.$

Change the scanf formats to "%lf"

You might also want to include math.h although it's not strictly necessary in this case.

Thank you very much!

Salem, so every time I wanna print a double variable, I need to use %lf instead of %f?

so every time I wanna print a double variable, I need to use %lf instead of %f?

The %lf is only required for scanf() for a double, which extracts the value from the stream, not print it. Unless you are using C99 or compiler specific extensions printf() uses %f for printing both float and double.

Jim

Originally Posted by jimblumberg

The %lf is only required for scanf() for a double, which extracts the value from the stream, not print it. Unless you are using C99 or compiler specific extensions printf() uses %f for printing both float and double.

Jim

I see. I tried using the %f for printing, and it worked, thanks!