The Runtime Stack

#include <stdio.h>

int ridiculous (int a, int b)
{
    static int c = 5;
    int d;
                                /* 3. Before calculation of d */
    d = c * (a + b);
                                /* 4. After calculation */
    return d;
}

int silly (int x)
{
    int y = 10;
    int z;
                                /* 2. Before the call to ridiculous() */
    z = ridiculous (x, y);
                                /* 5. After the call */
    return z;
}

int main ()
{
    int a, b, c;

    a = 2;                      /* 1. Before the call to silly() */
    b = silly (a);              
                                /* 6. After the call */
    c = a + b;
    printf ("c=%d\n", c);
}

Exercise 1: Compile and execute the above program.

• What is the output?
• If the parameter variable names in ridiculous (int a, int b) were re-named to ridiculous (int p, int q) (along with appropriate changes to the code inside ridiculous(), would the output change?
• If the static variable c in ridiculous() were re-named to m, would the output change?

Next, consider the six places (1-6, in comments) identified in the execution above. We will draw a (partial) snapshot of the runtime stack at these moments:

1. Stack contents at breakpoint 1:

   

2. Stack contents at breakpoint 2:

   

3. Stack contents at breakpoint 3:

   

4. Stack contents at breakpoint 4:

   

5. Stack contents at breakpoint 5:

   

6. Stack contents at breakpoint 6:

   

Exercise 2: Examine example2.c and draw detailed snapshots of the stack at various times in the program's execution.

Recursion