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:

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#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;

}

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What is wrong with this code?

Thanks in advance!

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

Eg.

Code:

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$ 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.$

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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?

Quote:

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

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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

Quote:

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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

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