给定两个整数a和b，编写一个函数来计算它们的和并返回该值。
a = 5
b = 10
# TODO: Write a function to calculate the sum of "a" and "b"
以下是Python的函数代码来计算两个整数的和：

```
def calculate_sum(a, b):
    return a + b

# Example usage
a = 5
b = 10
sum = calculate_sum(a, b)
print(sum) # Output: 15
```