Week 04 Tutorial Questions

Objectives

introducing MIPS data directives as a way to define and store globally-accessible data
introducing MIPS instructions that use and modify memory addresses
introducing the arithmetic needed to manipulate MIPS 1D arrays

Translate the following C program into MIPS assembler and run it with 1092 mipsy.

// Prints the square of a number

#include <stdio.h>

int main(void) {
    int x, y;
    printf("Enter a number: ");
    scanf("%d", &x);

    y = x * x;

    printf("%d\n", y);

    return 0;
}

Do the answer slowly and step by step. Have a plan before you start the question. Store variable x in register $t0 and store variable y in register $t1.

Write a MIPS assembler program that reads an integer and prints whether the number is odd or even. You should use a branch instruction to select the appropriate message.

#include <stdio.h>

int main(void) {
    int number;

    printf("Enter a number: ");
    scanf("%d", &number);

    if ((number & 1) == 0) {
        printf("Even\n");
    } else {
        printf("Odd\n");
    }

    return 0;
}

Translate this C program so it uses goto rather than if/else.

Then translate it to MIPS assembler.

// Squares a number, unless its square is too big for a 32-bit integer.
// If it is too big, prints an error message instead.

#include <stdio.h>

#define SQUARE_MAX 46340

int main(void) {
    int x, y;

    printf("Enter a number: ");
    scanf("%d", &x);

    if (x > SQUARE_MAX) {
        printf("square too big for 32 bits\n");
    } else {
        y = x * x;
        printf("%d\n", y);
    }

    return 0;
}

Translate this C program so it uses goto rather than if/else.

Then translate it to MIPS assembler.

#include <stdio.h>

int main(void) {
    int x;
    printf("Enter a number: ");
    scanf("%d", &x);

    if (x > 100 && x < 1000) {
        printf("medium\n");
    } else {
        printf("small/big\n");
    }
}

Translate this C program so it uses goto rather than if/else.

Then translate it to MIPS assembler.

// Print every third number from 24 to 42.
#include <stdio.h>

int main(void) {
    // This 'for' loop is effectively equivalent to a while loop.
    // i.e. it is a while loop with a counter built in.
    for (int x = 24; x < 42; x += 3) {
        printf("%d\n", x);
    }
}

Translate this C program so it uses goto rather than if/else.

Then translate it to MIPS assembler.

// Prints a right - angled triangle of asterisks, 10 rows high.

#include <stdio.h>

int main(void) {
    for (int i = 1; i <= 10; i++) {
        for (int j = 0; j < i; j++) {
            printf("*");
        }
        printf("\n");
    }
    return 0;
}

Translate this C program so it uses goto rather than if/else.

Then translate it to MIPS assembler.

// Simple factorial calculator - without error checking

#include <stdio.h>

int main(void) {
    int n;
    printf("n  = ");
    scanf("%d", &n);

    int fac = 1;
    for (int i = 1; i <= n; i++) {
        fac *= i;
    }

    printf("n! = %d\n", fac);
    return 0;
}

Write a MIPS assembler program that reads a non-negative integer and counts how many digits it contains. Your program should print the number of digits in the input number. You may assume that the input number is non-negative. Some examples are shown below:

Enter a number: 7
1

Enter a number: 42
2

Enter a number: 58392
5

Enter a number: 100000
6

The number 0 should be counted as having one digit:

Enter a number: 0
1

#include <stdio.h>

int main(void) {
    int number;
    int digit_count = 0;

    printf("Enter a number: ");
    scanf("%d", &number);

    if (number == 0) {
        digit_count = 1;
    } else {
        while (number > 0) {
            number = number / 10;
            digit_count++;
        }
    }

    printf("%d\n", digit_count);

    return 0;
}

Write a MIPS assembler program that reads a non-negative integer and prints the integer with its digits reversed. You may assume that the input number is non-negative. Some examples are shown below:

Enter a number: 7
7

Enter a number: 42
24

Enter a number: 58392
29385

Enter a number: 1000
1

Leading zeroes in the reversed number do not need to be printed. For example:

Enter a number: 1200
21

#include <stdio.h>

int main(void) {
int number;
int reversed = 0;

printf("Enter a number: ");
scanf("%d", &number);

while (number > 0) {
    int digit = number % 10;
    reversed = reversed * 10 + digit;
    number = number / 10;
}

printf("%d\n", reversed);

return 0;

}

Write a MIPS assembler program that implements a simple calculator. The program should read an integer, an operation, and another integer. The operation will be one of: - `+` for addition - `-` for subtraction - `*` for multiplication - `/` for integer division The program should calculate and print the result. You may assume that the input contains a valid operation and that the second number is not zero.

#include <stdio.h>

int main(void) {
    int number1;
    int number2;
    char operation;

    printf("Enter an expression: ");
    scanf("%d %c %d", &number1, &operation, &number2);

    if (operation == '+') {
        printf("%d\n", number1 + number2);
    } else if (operation == '-') {
        printf("%d\n", number1 - number2);
    } else if (operation == '*') {
        printf("%d\n", number1 * number2);
    } else if (operation == '/') {
        printf("%d\n", number1 / number2);
    }

    return 0;
}