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for loop

for 迴圈流程圖
$\begin{tikzpicture}[node distance=1.5cm]\setlength \baselineskip{1ex} \node [input,name=input] {}; \node [block, below of=input] (init) {init}; \node [decision, below of=init] (decision) {condition?}; \node [block, below of=decision] (code) {block code}; \node [block, below of=code] (increment) {increment}; \node [cir,below of=increment] (sum) {}; \node [output,below of=sum,name=output] {}; \path [line] (input) --(init); \path [line] (init) --(decision); \path [line] (decision) -- node[right]{true}(code); \path [line] (decision.east) -\vert node[right] {false} ($(decision.east) + (1.5,0)$) \vert- (sum.east); \path [line] (code) --(increment); \path [line] (increment) \vert- node[]{} ($(increment.west)+(-1.5,-1)$) \vert-(decision.west); \path [line] (sum) -- (output); \end{tikzpicture}$
語法：init 設定迴圈初始值，condition 判斷條件，increment 設定增減量。初始值不只設定迴圈控制變數的起始值，還可以設定其他變數的初始值。
```
for ( init; condition; increment )
{
   statement(s);
}
```

範例：輸入一數字，從 1 累加到輸入的數字。

[dywang@dyw219 zzz]$ vim for1.c 
[dywang@dyw219 zzz]$ cat for1.c 
#include <stdio.h>

main() {
	int i, a, sum=0;

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

	for ( i=1; i<a; i++) {
		printf("%d+", i );
		sum += i;
	}
	sum += i;
	printf("%d=%d\n", i,sum );
}

編譯成功

[dywang@dyw219 zzz]$ gcc -o for1 for1.c

執行結果

[dywang@dyw219 zzz]$ ./for1 
Enter an integer: 10
1+2+3+4+5+6+7+8+9+10=55
[dywang@dyw219 zzz]$ ./for1 
Enter an integer: 8
1+2+3+4+5+6+7+8=36

De-Yu Wang 2019-08-14