scanf（）不提示在stdin中输入

Question

#include <stdio.h>

int main(void) {
    float base, height, hyp;

    printf("input base of triangle:\n");
    scanf("%f", base);

    printf("input height of triangle:\n");
    scanf("%f", height);

    printf("input hypotenuse of triangle:\n");
    scanf("%f", hyp);

    float perimeter = base + height + hyp;

    printf("the perimeter of your triangle is: %f\n", perimeter);



    return 0;
}

I'm running this through ideone.com and it shows success, then standard input is empty, then in stdout it prints all my print statements with no numbers

Answer 1

This is because ideone is not interactive. Unlike running your program from the command line, ideone requires you to provide all the input upfront in the "input" tab:

You need to enter all your data before running your program.

PS Once you do, notice how you have undefined behavior because you pass values, rather than pointers, to scanf . The best way to address this on ideone is to pick "C99 strict" option when compiling your C code. This would break your compile with the following warning:

prog.c:7:11: error: format '%f' expects argument of type 'float *', but argument 2 has type 'double' [-Werror=format=]

  scanf("%f", base); 

Answer 2

scanf requires a pointer to your data type, you should pass the address of your variables using & :

scanf("%f", &base);
scanf("%f", &height);
scanf("%f", &hyp);

To add, some error checking might be useful, something like:

if(scanf("%f", &base) != 1) //number of items scanned is expected to be 1
  //process error..
//etc