C99 has a header file called <complex.h> which contains functions and macros to manipulate complex numbers. C99 also adds _Complex keyword to deal with complex numbers. But in this small program I have used C89 syntax and double data type to deal with complex numbers.
printf("\n\nThe format of Complex Number is a+bi\n\n");
printf("\nEnter the First Complex number: ");
printf("\nEnter the Second Complex number: ");
printf("\nThe Sum = %lf+%lfi\n",re3,im3);
Figure Below Shows a Sample Output