1 / 10

Conditional Statements

Conditional Statements. Topics if .. else For loop Do loop While loop. C code to Pseudo-C. C allows “ goto ” as means of transferring control Closer to machine-level programming style Generally considered bad coding style But, suitable for assembly programming. int max(int x, int y){

sun
Télécharger la présentation

Conditional Statements

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Conditional Statements • Topics • if .. else • For loop • Do loop • While loop

  2. C code to Pseudo-C • C allows “goto” as means of transferring control • Closer to machine-level programming style • Generally considered bad coding style • But, suitable for assembly programming

  3. int max(int x, int y){ if (x > y) return x; else return y; } if (t) then-statement; else else-statement; t = test_expr; if (!t) goto false; do then-statement; goto done; false: do else-statement; done: int goto_max(int x, int y){ int rval = y; int ok = (x <= y); if (ok) goto done; rval = x; done: return rval; }

  4. Branch Instructions • b (unconditional) • Conditional • beq, bne • bgez, bgtz, blez, bltz • bgezal bltzal • Set Condition • Sltz

  5. Conditional Branch Example int max(int x, int y) { if (x > y) return x; else return y; } # x in $a0, y in $a1 # return value in $t0 max: ble $a0, $a1, else or $t0, $a0, $0 jr $ra else: or $t0, $a1, $0 jr $ra t = test_expr; if (!t) goto false; do then-statement; goto done; false: do else-statement; done:

  6. C constructs broken into ‘goto’ • Example – Add an array • Pseudo Code – with ‘goto’ • More explicit in control of flow • Directly translated into Assembly code sum = 0; for (i=0; i<N; i++) sum += A[i]; printf(“Sum of array A is, %4d”,sum); sum = 0; i = 0; Rept: if (i >= N) goto Done sum += A[i]; i++; goto Rept Done: printf(“Sum of array A is, %4d”,sum);

  7. sum = 0; i = 0; Rept: sum += A[i]; i++; if (i < N) goto Rept printf(“Sum of array A is, %4d”,sum); .data A: .word 5:20 # 20-element array of initial values of 5 .text .globl main main: li $t0, 0 # $t0 <- sum li $a0, 0 # $a0 <- array index li $t9, 80 # array index upper bound in C context rept: lw $t2, A($a0) # $t2 <- value in the array add $t0, $t0, $t2 # sum += A[i] addi $a0, $a0, 4 # i++ in bytes blt $a0, $t9, rept ….

  8. Int lin_search(char x){ i=0; Retval = -1; while (i<72){ if (Tabchar_i,0]==x){ retval = Tabchar[i,1]; break; } else i++; }; return retval; } Lin_search: # x in $a0 li $t0,0 li $v0, -1 lin_rept: bge done, $t0, 72 bne else, $a0, $s0 lw $v0, Tabchar[I,1] b done else: addi $t0, $t0, 1(??) b lin_rept done: jr $ra }

  9. Initialize my own ‘free’ list struct node *list_init(int n) { struct node *free=NULL, *newp; for (i=0; i<n; i++) { newp=(struct node *) malloc(sizeof(struct node)); if (!newp) return NULL; else { newp->next = free; free = newp; } } return free; }

  10. struct node *list_init(int n) { struct node *free=NULL, *newp; for (i=0; i<n; i++) { newp=(struct node *) malloc(sizeof(struct node)); if (!newp) return NULL; else { newp->next = free; free = newp; } } return free; }

More Related