How can I convert a string number to a number in Perl?

MIPS User input string number, convert to integer?

• My assignment is prompt for a number string from the user, read the string (hint: syscall) given by the user, convert the string to an integer and store in register $s0. (do not have to worry about error checking for now). Then using syscall instruction, display the content of register $s0 to the console. This is what I have but I don't know how to convert to integer .text .globl __start __start: la $a0,str1 #Load and print string asking for string li $v0,4 syscall li $v0,8 #take in input la $a0, buffer #load byte space into address li $a1, 20 # allot the byte space for string move $t0,$a0 #save string to t0 syscall la $a0,str2 #load and print "you wrote" string li $v0,4 syscall la $a0, buffer #reload byte space to primary address move $a0,$t0 # primary address = t0 address (load pointer) li $v0,4 # print string syscall li $v0,10 #end program syscall .data buffer: .space 20 str1: .asciiz "Enter string(max 20 chars): " str2: .asciiz "You wrote:\n"

• Answer:

  You need to create a loop to inspect the characters of the string which will all be digits. You also need to know the length of the string. Map the ASCII value of each character to a binary value; e.g. 48 equals ASCII '0'. Your loop will need to increment over the length of the string, at the start of the loop you multiply the first character by 10^(n-1) and the last by 10^0. This is the same as saying that the 3 digit number 987=9*10*10 + 8*10 + 7. Each value you calculate will need to be dumped into a sum register. Note, you're going to have 2 nested loops; the first outer increments over the length of the string and finds your digit value. The second nested loop counts how many times you need to multiply your digit by 10. Since you're incrementing over the length of the string and DECREMENTING the number of times you need to multply your digit by 10, you're going to need 2 separate registers to store these index values. HINT: You can use your knowledge of ASCII for a nice shortcut. Rather than manually looking up each ASCII character value, since you know that an ASCII '0' is a decimal 48 and an ASCII '9' is a decimal 57, if you subtract 48 from the binary value of the character you'll get its numeric value. So, ASCII for '9' is 57, but minus 48==9.