Multiple statements in for loops in C++

By: Charles in C++ Tutorials on 2007-09-09

for statements are powerful and flexible. The three independent statements (initialization, test, and action) lend themselves to a number of variations.

A for loop works in the following sequence:

1. Performs the operations in the initialization.

2. Evaluates the condition.

3. If the condition is TRUE, executes the action statement and the loop.

After each time through, the loop repeats steps 2 and 3. Multiple Initialization and Increments It is not uncommon to initialize more than one variable, to test a compound logical expression, and to execute more than one statement. The initialization and the action may be replaced by multiple C++ statements, each separated by a comma. The program below demonstrates the initialization and increment of two variables.

Demonstrating multiple statements in for loops.

1:  //
2:  // demonstrates multiple statements in
3:  // for loops
4:
5: #include <iostream.h>
6:
7:  int main()
8:  {
9:      for (int i=0, j=0; i<3; i++, j++)
10:          cout << "i: " << i << " j: " << j << endl;
11:     return 0;
12: }

Output: i: 0  j: 0
i: 1  j: 1
i: 2  j: 2

Analysis: On line 9, two variables, i and j, are each initialized with the value 0. The test (i<3) is evaluated, and because it is true, the body of the for statement is executed, and the values are printed. Finally, the third clause in the for statement is executed, and i and j are incremented.
Once line 10 completes, the condition is evaluated again, and if it remains true the actions are repeated (i and j are again incremented), and the body of loop is executed again. This continues until the test fails, in which case the action statement is not executed, and control falls out of the loop