Tutorial: for loop in C vs Matlab

Introduction

There can be some confusion in translating a code from Matlab to C.

The most common mistake is in the for-loop syntax and index number.

Part 1. Iteration Counting

Iterate the loop 3 times

• Total number of iteration : N

// MATLAB
for k=1:N  fprintf ("hi");  end
    
// C-Prog:  Option 1
for (k=0; k<N; k++) printf ("hi");

// C-Prog:  Option 2
for (k=1; k<=N; k++) printf ("hi");
    

Example

Find the 2^4 = 16 (x=2, N=4)

int x=2;  int N=4;  int y = 1;

// MATLAB
for (k = 1:N)  y = y * x;  end

// C-Prog
for (int k = 0; k < N; k++)		y = y * x;

Part 2. Array Index

Use the array from the kth element, a total of N elements.

MATLAB: for k = kst : kend

• Index Start: Kst

• Total number of array : N

• Index End: kend= (N-1) + Kst

C-Prog: for (k = k0; k < Nmax; k++)

• Index Start: k0=Kst-1

• Total number of array : N

• Index End: kend= (N-1) + Kst

• Nmax= N+Kst

Problem 1: Use the array from the 1st element, a total of N=7 elements. (e.g. 10 to 70)

MATLAB:

• Index Start: kst=1

• Total number of array : N=7

• Index End: kend=7 // (7-1) + 1

  A = [10, 20, 30, 40, 50, 60, 70];

  for k = 1:7  	y=A(k);  end

C-Program:

• Index Start: k0=0 // 1-1

• Total number of array : N=7

• Nmax= 7 // 7+0

int A[7] = {10, 20, 30, 40, 50, 60, 70};

for (int k = 0; k < 7; k++)  y=A[k];

Problem 2: Use the array from the 3rd element, a total of 4 elements. (e.g. 30,40,50,60)

MATLAB:

• Index Start: kst=3

• Total number of array : N=4

• Index End: kend=6 // (4-1) + 3

for k = 3:6    	y=A(k);   end

C-Program:

• Index Start: k0=2 // 3-1

• Total number of array : N=4

• Nmax= 6 // 4+2

for (int k = 2; k < 6; k++)  y=A[k];