Hello Hope You Like The Project .. 

before Run The programe make sure to "Compile" it with any code editor or GCC..

in linux - 

if You use GCC Write the commad -
- Open Folder where file is located & Open Terminal there -Now-
1. gcc calculator.c -o  calculator
2. ./calculator

in windows -

Use DEVC++ paste the code and go to "Compile and Execute"

Done & Congratulation on making your Own calculator app usig c language..