Question

How to write an assembly program that simply counts how many A’s, C’s, T’s, and G’s the input string contain.

Answer 1

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.data
prompt: .asciiz "\nEnter a string: " #prompt for string
input: .space 1000 #string butter of 100 digit
.text
main:

li $v0, 4   
la $a0, prompt #prompt for string
syscall

li $v0, 8   
la $a0, input #ask for input
li $a1, 1000
syscall
move $s0, $a0 #move data to s0

li $t0,0 #count of C
li $t1,0 #count of T
li $t2,0 #count of A
li $t3,0 #count of G

loop: #loop while end of string
lb $a0, 0($s0) #load first character to a0
addi $s0, $s0, 1 #add index by one
beq $a0, $zero, done #else print character
sge $s5,$a0,'a' #check for lower case range
sle $s6,$a0,'z'
and $s5,$s5,$s6
beq $s5,1,lowercaseCount
j calculate
lowercaseCount:
sub $a0,$a0,32

calculate:
beq $a0,'C',cCount
beq $a0,'T',tCount
beq $a0,'A',aCount
beq $a0,'G',gCount
j exitCount
gCount:
add $t3,$t3,1 #c count ++
j exitCount
cCount:
add $t0,$t0,1 #c count ++
j exitCount
aCount:
add $t2,$t2,1 #c count ++
j exitCount
tCount:
add $t1,$t1,1 #c count ++
exitCount:

j loop
done:

li $a0,'C'
move $a1,$t0
jal printCount

li $a0,'T'
move $a1,$t1
jal printCount

li $a0,'A'
move $a1,$t2
jal printCount

li $a0,'G'
move $a1,$t3
jal printCount

li $v0,10
syscall

printCount:
move $v0,$a0 #print character
li $v0,11
syscall
li $a0,':' #print character
li $v0,11
syscall
move $a0,$a1 #print count
li $v0,1
syscall
li $a0,'\n' #print character
li $v0,11
syscall
jr $ra