Arrays Write a program that first reads in 20 integers and then asks the user whether they want to display all the even integers or all the odd integers.

Arrays Pseudo-code #include int main() { /* declare variables */ /* read in 20 integers */ /* Ask User */ /* display results */ return 0; }

Arrays Pseudo-code #include int main() { int i1,i2,i3,i4,i5,i6,i7,i8,i9,i10,i11,i12,i13, i14,i15,i16,i17,i18,i19,i20; int ans; printf(“Enter number 1: “); scanf(“%d”, &i1); printf(“Enter number 2: “); scanf(“%d”, &i2); … /* Ask User */ displayResults(ans,i1,i2,i3,i4,i5,i6,i7,i8,i9, i10,i11,i12,i13,i14,i15,i16,i17,i18, i19, i20); return 0; }

Arrays #include #define SIZE 20 int main() { int i[SIZE]; int cnt = 0, ans = 0; while( cnt < SIZE ) { printf(“Enter number %d: “, cnt+1); scanf(“%d”, &i[cnt] ); cnt++; } printf(“\nEnter 0=even, 1=odd: “); scanf(“%d”, &ans); displayResults(ans,i); return 0; } void displayResults( int ans, int nums[] ) { int i; for(i=0; i<SIZE; i++) if( ans ) if( nums[i]%2 ) printf(“%d “, nums[i]); else if( !(nums[i]%2) ) printf(“%d “, nums[i]); return; }

Arrays #include #define SIZE 20 int main() { int i[SIZE]; int cnt = 0, ans = 0; while( cnt < SIZE ) { printf(“Enter number %d: “, cnt+1); scanf(“%d”, &i[cnt++] ); } printf(“\nEnter 0=even, 1=odd: “); scanf(“%d”, &ans); displayResults(ans,i); return 0; } void displayResults( int ans, int nums[] ) { int i; for(i=0; i<SIZE; i++) if( ans ) if( nums[i]%2 ) printf(“%d “, nums[i] ); else if( !(nums[i]%2) ) printf(“%d “, nums[i] ); return; }

Arrays Referencing Arrays –identifier[index] –NOTE: index can be any expression Examples –int x[10]; –x[2+1] = 5; –x[3] = x[3] + num; (same as x[3] += num;) –x[5] = x[z] + x[3]; –sum = x[3] + x[f(r)];

Arrays Memory –int i[5]; –NOTE: Indexing starts with 0! i[0] i[1]i[2]i[3]i[4]

Arrays Initializing arrays –datatype identifier[array_size] = { init list }; Examples –int x[3] = { 2, 4, 8}; –char v[] = { ‘a’, ‘e’, ‘i’, ‘o’, ‘u’ }; 248 x[0] x[1]x[2] aeiou v[0] v[1]v[2]v[3]v[4]

Functions, Arrays, and Pointers call-by-reference –Array int f(int n[]); int x[5]; f(x); int f(int n[]); int x[5]; f(&x[0]); int f(int *n); int x[5]; f(x); int f(int *n); int x[5]; f(&x[0]); –Why are these all equivalent?

Functions, Arrays, and Pointers Main Data Area x Function f data Area n

Functions, Arrays, and Pointers Pointer and Array equivalence int x[] = {1,2,3,4,5,6,7,8,9,10}; int *y; y = x; *y = x[3]; *x = y[6]; y[4] = *x; y = &x[4]; *y = x[9]; for (i = 0; i < 10; i++) printf(“%d “, x[i]);

Arrays #include #define SIZE 20 int main() { int i[SIZE]; int cnt = 0, ans = 0; while( cnt < SIZE ) { printf(“Enter number %d: “, cnt+1); scanf(“%d”, &i[cnt++] ); } printf(“\nEnter 0=even, 1=odd: “); scanf(“%d”, &ans); displayResults(ans,i); return 0; } void displayResults( int ans, int nums[] ) { int i; for(i=0; i<SIZE; i++) if( ans ) if( nums[i]%2 ) printf(“%d “, nums[i] ); else if( !(nums[i]%2) ) printf(“%d “, nums[i] ); return; }