midterm review

ECE 15

Grant R. Vousden-Dishington

Fall 2013

Data types

char

(single) character

integer values

float

single-precision floating point number

double

double-precision floating point number
twice as much memory as float

These are 'numerical' data types

Variables & names

Data is assigned to memory using the assignment operator (=)

and referenced through the use of variables

Names may ONLY contain alphanumeric characters and underscores

Names may NOT begin with numbers

Printing and scanning

%c - char
%d - int
%f - float
%lf - double

Stands for 'long float'

special characters

single space

'\t'

tab space

'\n'

new line

'\b'

backspace (i.e. delete one character, move back one space)

'\0'

null character
same as '', two single quotes with no space between

Conditional Statements

if(CONDITIONAL)     x++;

Increments x only if CONDITIONAL is TRUE

if(CONDITIONAL)    x++;else    x--;

Increments x if CONDITIONAL is TRUE, decrements otherwise

if(CONDITIONAL) {    x++;
    printf("Why is the midterm hand written?");}else    x--;

Need to enclose multiple lines in { }

Switch-Case Statements

Just another form of if-else

int x;scanf("Gimme an x: %d", &x);

switch(x%2)
{
    case 0: printf("x is even.");    case 1: printf("x is odd.");    default: printf("I don't know what that is but I don't like it.");}

// Same as the above, using if-else structure
if(x%2 == 0)
    printf("x is even.");
else if(x%2 == 1)
    printf("x is odd.");
else
    printf("I don't know what that is but I don't like it.'"

Loops

for(THINGS_TO_DO_ONCE; CONDITIONAL; THINGS_TO_DO_EVERY_LOOP)
while(CONDITIONAL)

100% interchangeable - anything one can do, the other can do

Same rules about { } as if-else statements

No 'else' statements for loops (in C)

1-D Arrays

int myArray[10]; // Declares an array of 10 integers
myArray[0] = 5; // Sets the FIRST element of the array to 5
myArray[1] = 7; // Sets the SECOND element of the array to 7
// Print out all the values in myArrayfor(int i = 0; i < 10; i++)    printf("%d ", myArray[i]); // prints out all the elements of the array
// Short way to scan values into the arrayi = 0;while(scanf("%d", &myArray[i++]) > 0);

// This works toofor(i = 0; i < 10; i++)    scanf("%d", &myArray[i]);

PRACTice

Output 1

int i1 = 5, i2 = 10;
double d1 = 5.0, d2 = 10.0, d3;
d3 = i1/i2;
printf("line 1: %d\n, i1/i2);
printf("line 2: %.1lf\n", d1/d2);
printf("line 3: %.1lf\n", i1/d2);
printf("line 4: %d\n", (int)d1/i2);
printf("d3 = %.1lf\n", d3);

line 1: 0
line 2: 0.5
line 3: 0.5
line 4: 0
d3 = 0.0

Output 2

int x = 0, y = 0, i = 1, j = 1;
for (i = 0; i < 4; i++)
{
    x = i;
    for (j = 0; j < 10; j++)
        y +=x;
}
printf("x = %d y = %d i = %d j = %d", x, y, i, j);

x = 3 y = 60 i = 4 j = 10

Output 3

int x = 2, y = 1;
switch(x+y)
{
    case 1: x+=1;
    case 2: x+=2; break;
    case 3: x+=3;
    case 4: x+=4; break;
    default: x+=5;
}
printf("x = %d\n", x);

 x = 9

Output 4

int i, x = 0;
for (i = 1; i < 6; i++)
{
    if (i%2 == 0) continue;
    if (i == 4) break;
    x++;
}
printf("i = %d x = %d\n", i, x);

i = 6 x = 3

Output 5

double x = 5.2, y = 3.8, z = -5.2, w = -3.8;
int x2 = (int) (x + ( x < 0 ? -0.5 : 0.5) );
int y2 = (int) (y + ( y < 0 ? -0.5 : 0.5) );
int z2 = (int) (z + ( z < 0 ? -0.5 : 0.5) );
int w2 = (int) (w + ( w < 0 ? -0.5 : 0.5) );
printf("x2 = %d y2 = %d z2 = %d w2 = %d", x2, y2, z2, w2);

x2 = 5 y2 = 4 z2 = -5 w2 = -4

Output 6

int x = 0, y = -1, z = 1;
x-- || ++y && z++;
printf("x = %d y = %d z = %d\n", x, y, z)


x = -1 y = 0 z = 1

int x, y, z; 
x = y = 1; 
z = 0; 
x-- || y-- && z++ ; 
printf(“x = %d y = %d z = %d\n”, x, y, z);


x = 0 y = 1 z = 0

Program Rewriting

#include <stdio.h>
int main()
{
    int i, j;
    for (i = 3; i > 0; i--)
    {
        for (j = 0; j < i; j++)
            printf("*");
        printf("\n");
    }
    return 0;
}


        ***
        **
        *

#include <stdio.h>
int main()
{
    int i, j;    i = 3;
    while(i > 0)
    {        j = 0;
        while(j < i)        {
            printf("*");            j++;        }
        printf("\n");        i--;
    }
    return 0;
}

Program reWriting

Write the code that prints the following, using nested loops

|*****||**** ||***  ||**   ||*    |

 for(int i = 5, j; i > 0; --i){    printf("|");    for(j = 0; j < 5; j++)        printf("%c", j < i ? '*' : ' ');    printf("|\n");}

Write your own code

A number n is a perfect number if its factors, including 1, but not including the number itself, sum to n. For example, 6 is a perfect number, because the factors of 6 (not including 6) are 1, 2 and 3, and 1 + 2 + 3 = 6. 28 is also a perfect number, because 1 + 2 + 4 + 7 + 14 = 28. Write code to print out all of the perfect numbers between two values entered by the user, where the first number entered is the starting point of the range, and the second number entered is the ending point of the range. Your code should check to make sure that the numbers entered by th user are strictly positive, and that the second number is larger than the first number. You may assume the user enters integer values. After printing all of the perfect numbers between (and including) the values entered by the user, your code should either print out “No perfect numbers in range” or a message indicating the quantity of perfect numbers that were in the range. Note that the word printed in the final message is either “number” or “numbers” depending on whether 1 or more perfect numbers were found, but the line listing the perfect numbers always says “Perfect numbers are:”

Write your own code

A number n is a perfect number if its factors, including 1, but not including the number itself, sum to n. For example, 6 is a perfect number, because the factors of 6 (not including 6) are 1, 2 and 3, and 1 + 2 + 3 = 6. 28 is also a perfect number, because 1 + 2 + 4 + 7 + 14 = 28. Write code to print out all of the perfect numbers between two values entered by the user, where the first number entered is the starting point of the range, and the second number entered is the ending point of the range. Your code should check to make sure that the numbers entered by the user are strictly positive, and that the second number is larger than the first number. You may assume the user enters integer values. After printing all of the perfect numbers between (and including) the values entered by the user, your code should either print out “No perfect numbers in range” or a message indicating the quantity of perfect numbers that were in the range. Note that the word printed in the final message is either “number” or “numbers” depending on whether 1 or more perfect numbers were found, but the line listing the perfect numbers always says “Perfect numbers are:”

Common midterm mistakes

Missing '&' using scanf and using '&' in printf
Forgetting to increment/decrement value with ++ and --
Missing scanf or printf all together
Using < when should use <=, or vice-versa

Makes you do one more or less loop than you should've

Using wrong number of loops

Use loops to get multiple user inputs, print multiple rows or columns

RUSHING through the easier problems
Not writing ANYTHING

At least declare, scan and print your variable

Not sleeping