CSC 107 – Programming For Science

Today’s Goal  Discover best uses of structures in a program  How we can mix pointers inside structures  Assigning struct s & what this means for pointers  Do struct s have an address? How can we get this?  Pointers to struct s & operators who love them

Like, But Better  Single value is enough to describe some data  In real-life, however, this is not very common  For everything else, there are struct s  Groups values together using 1 or more fields  Within struct, each field has name & type  Variables are variables even if of struct type  Each variable has own copy of every field in struct  Copy values when assigning one struct to another

How Do struct s Work?  These work just like a real-life blueprint  Blueprint creates items with same layout (fields)  Use as often (or as little) as want; cannot wear it out  Making change to one item does not affect others

Creating A struct

Assigning struct s  Like all variables, can assign struct s  Identical struct type needed for source & target  Works like assigning fields in source to fields in target  Primitive values are copied like primitive variables  With assignment, arrays & pointers alias same value  Fields just like variables of the same type  Can be used just like any variable of that type  Need struct to get access to the field initially

Using struct s As Parameters  Functions can use struct as a parameter  Must pass same struct type for the argument  Parameter assigned (copies) argument passed in  Field values duplicated like all struct assignments  Call will not & cannot change fields’ values  Like passing any variable as argument to a function  But, like normal, entries in array field may change

Functions Returning struct s  Like all types, functions can return struct  Return type specifies struct type to be returned  Function SHOULD use return statements to end  Works like any other return type we used so far  Nothing to see here; world continues to rotate  Easy updating struct parameter using this process struct energy drop(struct energy dropMe); // Lots of (pretend) code here for you to imagine struct energy bar, foo = { 34.5, 23.3 }; bar = drop(foo);

Pointers to struct

Will It Compile? struct momentum { double mass, velX, velY; }; struct momentum rock = { 13, 1, 4 }; struct momentum projectile; struct momentum arr[10]; struct momentum *ptr = &rock; projectile = arr[4]; arr[2] = ptr; arr[5].mass = 7; (*ptr).velX = pow(arr[1].velY, 2); arr[5] = *ptr; arr[1].velX = ptr->mass; ptr = &arr; (&projectile)->velY = rock->velX + rock->velY; *ptr = new struct momentum[100];

Will It Compile? struct momentum { double mass, velX, velY; }; struct momentum rock = { 13, 1, 4 }; struct momentum projectile; struct momentum arr[10]; struct momentum *ptr = &rock; projectile = arr[4]; arr[2] = ptr; arr[5].mass = 7; (*ptr).velX = pow(arr[1].velY, 2); arr[5] = *ptr; arr[1].velX = ptr->mass; ptr = &arr; (&projectile)->velY = rock->velX + rock->velY; *ptr = new struct momentum[100];

Will It Compile? struct momentum { double mass, velX, velY; }; struct momentum rock = { 13, 1, 4 }; struct momentum projectile; struct momentum arr[10]; struct momentum *ptr = &rock; projectile = arr[4]; arr[2] = ptr; arr[5].mass = 7; (*ptr).velX = pow(arr[1].velY, 2); arr[5] = *ptr; arr[1].velX = ptr->mass; ptr = &arr; (&projectile)->velY = rock->velX + rock->velY; *ptr = new struct momentum[100];

Will It Compile? struct momentum { double mass, velX, velY; }; struct momentum rock = { 13, 1, 4 }; struct momentum projectile; struct momentum arr[10]; struct momentum *ptr = &rock; projectile = arr[4]; arr[2] = ptr; arr[5].mass = 7; (*ptr).velX = pow(arr[1].velY, 2); arr[5] = *ptr; arr[1].velX = ptr->mass; ptr = &arr; (&projectile)->velY = rock->velX + rock->velY; *ptr = new struct momentum[100];

Will It Compile? struct momentum { double mass, velX, velY; }; struct momentum rock = { 13, 1, 4 }; struct momentum projectile; struct momentum arr[10]; struct momentum *ptr = &rock; projectile = arr[4]; arr[2] = ptr; arr[5].mass = 7; (*ptr).velX = pow(arr[1].velY, 2); arr[5] = *ptr; arr[1].velX = ptr->mass; ptr = &arr; (&projectile)->velY = rock->velX + rock->velY; *ptr = new struct momentum[100];

Will It Compile? struct momentum { double mass, velX, velY; }; struct momentum rock = { 13, 1, 4 }; struct momentum projectile; struct momentum arr[10]; struct momentum *ptr = &rock; projectile = arr[4]; arr[2] = ptr; arr[5].mass = 7; (*ptr).velX = pow(arr[1].velY, 2); arr[5] = *ptr; arr[1].velX = ptr->mass; ptr = &arr; (&projectile)->velY = rock->velX + rock->velY; *ptr = new struct momentum[100];

Will It Compile? struct momentum { double mass, velX, velY; }; struct momentum rock = { 13, 1, 4 }; struct momentum projectile; struct momentum arr[10]; struct momentum *ptr = &rock; projectile = arr[4]; arr[2] = ptr; // Should be *ptr arr[5].mass = 7; (*ptr).velX = pow(arr[1].velY, 2); arr[5] = *ptr; arr[1].velX = ptr->mass; ptr = &arr; (&projectile)->velY = rock->velX + rock->velY; *ptr = new struct momentum[100];

Will It Compile? struct momentum { double mass, velX, velY; }; struct momentum rock = { 13, 1, 4 }; struct momentum projectile; struct momentum arr[10]; struct momentum *ptr = &rock; projectile = arr[4]; arr[2] = ptr; // Should be *ptr arr[5].mass = 7; (*ptr).velX = pow(arr[1].velY, 2); arr[5] = *ptr; arr[1].velX = ptr->mass; ptr = &arr; (&projectile)->velY = rock->velX + rock->velY; *ptr = new struct momentum[100];

Will It Compile? struct momentum { double mass, velX, velY; }; struct momentum rock = { 13, 1, 4 }; struct momentum projectile; struct momentum arr[10]; struct momentum *ptr = &rock; projectile = arr[4]; arr[2] = ptr; // Should be *ptr arr[5].mass = 7; (*ptr).velX = pow(arr[1].velY, 2); arr[5] = *ptr; arr[1].velX = ptr->mass; ptr = &arr; (&projectile)->velY = rock->velX + rock->velY; *ptr = new struct momentum[100];

Will It Compile? struct momentum { double mass, velX, velY; }; struct momentum rock = { 13, 1, 4 }; struct momentum projectile; struct momentum arr[10]; struct momentum *ptr = &rock; projectile = arr[4]; arr[2] = ptr; // Should be *ptr arr[5].mass = 7; (*ptr).velX = pow(arr[1].velY, 2); arr[5] = *ptr; arr[1].velX = ptr->mass; ptr = &arr; (&projectile)->velY = rock->velX + rock->velY; *ptr = new struct momentum[100];

Will It Compile? struct momentum { double mass, velX, velY; }; struct momentum rock = { 13, 1, 4 }; struct momentum projectile; struct momentum arr[10]; struct momentum *ptr = &rock; projectile = arr[4]; arr[2] = ptr; // Should be *ptr arr[5].mass = 7; (*ptr).velX = pow(arr[1].velY, 2); arr[5] = *ptr; arr[1].velX = ptr->mass; ptr = &arr; (&projectile)->velY = rock->velX + rock->velY; *ptr = new struct momentum[100];

Will It Compile? struct momentum { double mass, velX, velY; }; struct momentum rock = { 13, 1, 4 }; struct momentum projectile; struct momentum arr[10]; struct momentum *ptr = &rock; projectile = arr[4]; arr[2] = ptr; // Should be *ptr arr[5].mass = 7; (*ptr).velX = pow(arr[1].velY, 2); arr[5] = *ptr; arr[1].velX = ptr->mass; ptr = &arr; // Should be arr (&projectile)->velY = rock->velX + rock->velY; *ptr = new struct momentum[100];

Will It Compile? struct momentum { double mass, velX, velY; }; struct momentum rock = { 13, 1, 4 }; struct momentum projectile; struct momentum arr[10]; struct momentum *ptr = &rock; projectile = arr[4]; arr[2] = ptr; // Should be *ptr arr[5].mass = 7; (*ptr).velX = pow(arr[1].velY, 2); arr[5] = *ptr; arr[1].velX = ptr->mass; ptr = &arr; // Should be arr (&projectile)->velY = rock->velX + rock->velY; *ptr = new struct momentum[100];

Will It Compile? struct momentum { double mass, velX, velY; }; struct momentum rock = { 13, 1, 4 }; struct momentum projectile; struct momentum arr[10]; struct momentum *ptr = &rock; projectile = arr[4]; arr[2] = ptr; // Should be *ptr arr[5].mass = 7; (*ptr).velX = pow(arr[1].velY, 2); arr[5] = *ptr; arr[1].velX = ptr->mass; ptr = &arr; // Should be arr (&projectile)->velY = rock->velX + rock->velY; *ptr = new struct momentum[100]; // Should be ptr =

Tracing Pointers to struct struct energy { double mass, potent, kinet; }; struct energy ball; struct energy * projectile = &ball; ball.mass = 100; ball.kinet = 0; ball.potent = ball.mass * 10 * 10; for (int i = 0; i kinet = ball.mass * 10 * i; cout <<“v=” << sqrt(ball.kinet*2/ball.mass)<<endl; }

Your Turn  Get into your groups and try this assignment

For Next Lecture  Using struct s in real programs in  When would struct s be created in real program?  How do we combine struct s for best use?  How are typedef s used in the real world?  Weekly Assignment #12 still out, but due in 8 days  Last programming assignment  Last programming assignment available in Angel